Brushes allow a designer to duplicate the look of physically operated paint brushes on a computer. This blend of science and art is so highly refined, that a brush’s precise qualities are duplicated, like thickness, brush angle, pressure, ability to daub, streaking, and more. Advanced brushes allow a designer to mix and blend colors, exactly as they would with oil paints or pastels. Good digital brushes even duplicate real-life wear and drying, so the effect this has on artworks is retained. The result is great art without dirty clothes or turpentine, granting those things have their own romantic charm.

RetroSupply Co. is the perfect starting point to explore brushes. Warning: Retro’s astounding products might distract you. You might want to try all of them simultaneously. That might sound rhetorical, but in fact, RetroSupply Co. is an astounding achievement that we are proud to be associated with. But first, this is how you install digital brushes.

And here is an excellent reiteration from Adobe:

How to Import brushes into the Brushes panel from another file

1. Choose Window > Brushes Libraries > Other Library and select the file (expand the zip file downloaded from YouWorkForThem and locate the AI file(s)).
2. In the Brush Library panel, click on the individual brush definition or all the brush definitions that you need to import and select Add To Brushes from the Brush Library panel menu (flyout menu).