Painter Classic has a very simple interface. The outcome and effect mostly depends on how well you know these controls.

The Toolbox

These are the tools that provides the basic functions in Painter, such as the Magnifiers, Grabber, Marquee, Lasso, etc. To start drawing, the Brush is selected. Only after selecting the Brush tool, the options chosen in the below Brush box will take effect.

The Brushes

These are the Brushes available in Painter, where most of the time I use only the Pencil, Eraser and Water Color tools.

For Painting, the Water Color is all I really use. I prefer this over other brushes because it creates a wet layer of paint on top of the lineart. To erase wet paint, a Wet Eraser is used. The Wet Eraser could be found by further expanding the Water Color Menu. (where 'Medium' is written) 'Medium' is just one of the sub-tools in Water Color.

By having a difference of Wet Paint and Dry Lineart, it'll just be like painting with Layers, where in this case it's only two.

The Brush Control

This is the Brush Control that enables you to determine the details of the brush. Everytime I select a brush, I tinker with the Size, Opacity and Grain. Painter Classic has the bad habit of not remembering the last used positions of the bars everytime I select the same brush over again. But yeah, you get used to it after a while.

Size controls the thickness of the stroke, or in other words, the size of the brush.

Opacity controls the denseness and strength of the stroke. Yeah, you could do the same if you're using a pressure-sensitive tablet, but Opacity comes in handy when you're trying to do washes or shading with Water Color.

Grain controls the surface of the canvas, on how much of the paint stick to the canvas, etc. Most of the time I just set it to zero to get my colors out bold and bright. Only when I want to apply Paper texture to the painting, I set the Grain to a value other than 0.

The Material Box

This is pretty self-explanatory. The Color tab allows you to select the color you want. The Paper sets the type of texture you want on your canvas. The rest (Grad, Pattern, Nozzle) I don't use in my CGs so I'll skip them.