The paintbrush works much like the pencil tool except that it paints an anti-aliased line that blends with the background.

Like the pencil tool, you have all the regular brush options as well as the opacity and Fade options. Try them out to see the effects of the options on anti-aliased lines.

Besides the usual cast of options, the paintbrush also has a "Wet Edges" option in the Options palette which when checked, causes the paintbrush to create a translucent line with darkened edges similar to water color painting.