There are different tools you can use to draw:
At the beginning of the game, the pencil and the eraser will be available in their most basic form. They will both only have one stroke available, and the pencil will only come in four colors.
You'll be able to see the tool's level, as well as its color and stroke, in the tools tab located at the bottom of the screen. Every tool will reach a maximum level of 10, except for the eraser and the zoom, which will reach a maximum level of 4.