First button: Draw (or brush) . An old thing that you make something.
Second button: Spray. Makes a drawing that looks like dots. The bigger the spray size it gets. The more the dots get. It can be used for realistic things or horror games.
Third button:Shape drawer/Shape brusher. Makes a drawing with shape available on it. You can even duplicate drawings too.
Fourth button:Filler.Fills any hole that are remaining. Also in Shapes mode.
Fifth button: Move. Moves the drawing where youre using on the layer. But you can control the size of the drawing. And also it is in Shapes.
Sixth button: Eraser. Erases drawings. Also in Shapes mode.