The GIMP interface is easy to understand. On the left there are the drawing tools and, below them, the options for the selected tool, while on the right there are the layers and, below them, brushes and other stuff.
As a start, let's create a new file! Go
file>new, then select the dimension of the image. I advise to create big pictures, they will be easier to edit and can be resized later. A 2000x2000 px should be enough.
NOTE = if you select the "advanced options" you can set the background to be transparent (just select "transparent" where it says "fill with"). You can leave it white if you like, because we're not going to work in the background layer.
IMPORTANT = the first thing you should do now is saving the file, and remember to save often so you won't lose any progress if something goes wrong!
You need to create a new layer with
layer>new layer. Name it "Lineart" and be sure the option "transparency" is selected, then click ok.
VERY IMPORTANT = every layer created from now on must have the option "transparency" selected!
Now, while this layer is selected, you can start drawing.
Select the "Pencil Tool" and then tick the option "Smooth Stroke" and set "Quality" to 100 and "Weight" to around 200. This way you will have a better control of the tool and the lines will come out much smoother.
(If you never used this option before, I suggest gaining some exp point with it drawing random lines). You can change their values accoring to your style.
Now you can draw your adoptable the best you can. If you want, you can use another layer to make a rough sketch, and then the Lineart layer to draw the lines you will use in your adoptables.
Once you drew the sketch on a new layer, you can decrease its opacity to better see what you're drawing in the Lineart layer.
You can also lower the size of the pencil to add some details to your adopt.
When you're done, hide the "Sketch Layer" to have a look at your lineart.
