At the request of workers, I am writing a guide on Paint Tool SAI.
I will mainly analyze brush settings and other purely technical issues. And, as they say, from scratch. :)
As for anatomy, construction and other things, I recommend this selection on Equestria Daily, because my pony proportions are non-canonical and in general the author’s style is in all fields. :)
So... (be careful, there are quite a lot of letters and pictures under the cut)

We start, as usual, by creating a new file. File>New or Ctrl+N, everything is standard.
It is better to set the file size larger, 2000x2000 or more (depending on the capabilities of the computer), Resolution no less than 300 pixel/inch, so that you can safely draw small details without soap and pixelation. In the end, a raster image that is too large can easily be reduced or cropped, but the consequences of stretching a small one will most likely be sad.
So, we have a blank canvas and toolbars. Now a little about them:

Navigation.

Everything is simple here - navigation window, zoom (slider and +, - and reset buttons) and canvas rotation (the functions are the same).

Layers.

Subsection Paints Effect allows you to set the texture and effect for the selected layer.
In the drop down menu Mode you can select the mode in which the layer will interact with the underlying ones.
Here, for example, is what the same blue line will look like when changing the parameters of the layer on which it is located:

Opacity, respectively, sets the transparency of the selected layer.
Combinations of blending mode and transparency are very useful for creating various effects. For example, for drawing sun rays you can take a luminosity layer with low transparency (10 percent). Thus, the drawn rays will not overlap the objects in the picture, but will only softly highlight them.
In general, this is one of those features that is best understood at random. You can create an interesting effect completely by accident. :)
Below is a list of layers. They can be swapped by dragging and hidden by clicking on the “eye” icon next to the layer name. The active layer is highlighted in lilac.

Colors.

Everything is simple here - the color selection panel. If it did not appear when you first launched it, select Window>Color Wheel from the menu.

Controls and selected colors.

Here, too, everything is standard - rectangular selection, free selection, “magic wand”, moving a layer or selected area, rotation, “hand” for moving and “eyedropper” for selecting colors.

Brushes and their settings.

But here it is worth stopping in more detail. Of course, SAI has a set standard tools, but it is not necessary to use them “as is”. Each of them is freely customizable to the needs of the painter.

The first in the list is the blend mode (similar to the layer blend mode) and the choice of egde shape - the shape of the edges of the brush.
These “brush edges” allow you to give your stroke a defined shape or make it blurry:

Then adjust the brush size - Size. Here, I think, everything is clear.
Next - MIn. Size, minimum size. When drawing on a tablet, the pen responds to pressure, so you can control the thickness of the line. At minimum size brushes at 0%, the thickness of the line will vary from very thin to the maximum (that is, the size specified above), at 100% it will not change at all.

The Density parameter sets the transparency of the line.

Next there are two drop-down menus in which you can select the shape of the brush (the default is simple circle) and the texture for it (accordingly, the default is no texture).

The next three options are Blendind, Dilution and Persistence.
Blending controls how well the brush color blends with other colors on the layer.


Dilution“thin” the paint. That is, at the maximum value of this parameter, the color will begin to appear only when mixed with nearby shades.


Persistence is responsible for the “fastness” of color when mixed.

Check mark "keep opacity" is responsible for whether the standard background is considered white or “transparent”. This will affect the mixing of paints. As far as I know, it works slightly differently in different versions programs.

Then they go "Advanced settings":
Quality- is responsible for the quality of stroke development. Of course, it is better to set this parameter to maximum, but on a weak computer this will cause lags or even freeze the program (especially if a large brush size is selected).
Egde Hardness- clarity of stroke edges.
Min density- minimal transparency. This option allows you to have more control over the transparency of the line.
Max Dens Prs- the same, but adjusts the dependence of transparency on the pressure of the tablet pen. That is, if you set this parameter to 0, then even with the weakest pressure on the pen, SAI will produce the most opaque line. 100% of the time you will have to press down on the pen to do this.
Hard - Soft adjusts pen sensitivity.
Checkmarks "Dens", "Size" And "Blend" You can mark the actions for which pressing the pen is responsible. If they are all checked, pressing harder makes the stroke less transparent, as wide as possible, and allows you to adjust the degree of color blending. Dens means transparency, size means size, and blend means blending.

Some useful keyboard shortcuts and other trivia
Ctrl+T - transform the selected fragment. If nothing is selected, the entire layer is taken. To apply the transformation, you need to press Enter, to cancel - Esc.
Ctrl+E - merge the active layer with the previous one. Convenient at the “finish line” when you need to process various small details and correct jambs.
As for mistakes, there is one trick that can help you see your mistakes if your eyes are blurred. The Canvas menu has a Flip Hoizontally feature that mirrors your drawing. Problems with the construction become immediately apparent. Maybe not all of them, but definitely the rudest ones.
SAI, of course, does not have large set filters, but the Filter>Hue and Saturation function can help in adjusting the color scheme. Also, as I already said, you can use different layers with low transparency - this sometimes gives unexpected results. :)

Well, it seems like the basic functions are listed. :)
I hope this impromptu guide will help in some way. If you have questions, comments or bugs, write in the comments.
If necessary, I can try to write a more specific guide on painting, working with layers, etc.

Good evening, friends!

The guide was created for the sake of interesting things in Paint tool Sai or simply Sai.
Here I will tell you about the possibilities in this program. First of all, I want to talk about brushes. Brushes in Sai can be customized for any drawing subject. In this guide I will talk about a pencil. After all, many people love art drawn with a pencil, but in Sai it’s like times available.

Paint tool Sai. Just click

So let's get started. How to set up a brush for a regular pencil? It’s all very simple, just use the settings of a regular Pen brush or another. Catch your thoughts and take the pen to draw!
Pencil brush settings. English version and Russian


I'll tell you more interesting things later.
Today I will also tell you about “Outline Selection”.
Actually, what is this for? Of course, to quickly select a contour and save time. For this, I will give you an interesting explanation and settings.
First of all, let’s select the contour itself, and then remove our “details” that were formed during selection, using SelPen tool. However, if you go beyond the line, this is fixable. You can simply take the SelEras tool and remove everything.

For example, I will use the lineart of my OS

Step 2: Paint the area inside the line art

You can do this by taking a pen and starting to paint by hand, but this will take a long time. I'll show you a way to save your precious time
Go to the line art layer and select "Selection source" just above in the layers window. Your layer will be highlighted in green.

Then make a new layer under your line art and fill it with some color using the Bucket tool. A bright color will work better.

Now select the Wand tool. In the settings under the tools you will see something like “Detection mode” and “Target”. Select "Transparency (strict)" and "Selection source". Set the transparency slider to the minimum value or even zero.

Go back to the layer that you filled with bright color and click with the Magic Wand tool somewhere outside the line art. This area will turn blue (Blue in SAI shows the selection area).

Clue:
If something is also selected inside the line art, press CTRL+D (deselect) and try setting the transparency value on the slider to a lower value. If the transparency is already at zero, then there is a gap in the outline of your line art and you need to close it if you want to work in this technique.

Now press CTRL+X

Now you should check the result and manually erase any imperfections on the small details of the line art.


Now your line art is colored and it's time to move on to the main colors.

Step 3: Clipping the Layer

What is layer clipping? When a layer is clipped by another layer, it occupies the same transparent areas as the one underneath it. This means that if you draw something on the bottom layer and then start drawing on the top layer, it will only show the visible area from the bottom layer.

Now to apply the main colors to the line art, create layers on top of the bright color layer and assign them a “clipping group”. Your layers with paint will be cut off by a layer with a bright color and no matter how carefully you apply paint, it will still not go beyond the line art

Hello! Now I will tell you how to paint in sai without going over the edges.

First, I’ll show you my brush settings for the line (in case someone needs it)

So let's get started!

Let's say you've drawn a line and you need to color it. Create a new layer under the line.

Select the Selection tool (aka the magic wand)

And be careful about the settings of this tool. If your line is translucent or has burrs, then you should choose a lower value. If you have a straight line by hand or vector, then you can choose the average value.

Select on the line layer the place that we need to paint

Notice that we still have unpainted areas a couple of pixels in size. Sometimes they may be, sometimes not. It all depends on the meaning of the Magic Wand tool. It is individual for each drawing. But since this happened to us, we select the manual selection tool

And paint over all the edges to make it neat

Now choose the tool you are going to paint with

And paint the selected area ON AN EMPTY LAYER UNDER THE LINE(!)

Then on the same layer we press the Fix Opacity button

Now you can paint this piece without going over the edges! This can also be done with a simple selection, but this dotted line is an eyesore for many, so you can use this method.

You can paint the line in the same way, if something happens:

Thanks for reading!