This information applies to Adobe Photoshop CC 2019 through Photoshop 2022.
These custom brushes are accessed in the Brushes menu.
Free Photoshop brushes are easy to find online.

Brusheezy
Popular places to find brushes includeDeviantArt,Brusheezy, and Tumblr.
Photoshop Brush files use the.abr extension.
Launch Photoshop and create a new file or open an existing one.

From theBrusheswindow, smack the three-line hamburger icon to reveal a flyout menu.
If the Brushes window isn’t visible, go to theWindowmenu and selectBrushes.
fire up the ABR file of the brush or brush pack, then selectLoad.

The new brush (or brush pack) displays in the Brushes window.
Select and use a tool from this new grouping.
Custom brushes behave identically to stock brushes.

Brusheezy
The Adobe Stock service offers thousands of brushes.
These brushes do, however, plug in cleanly with Photoshop.