If you've downloaded the .abr file and don't know what to do next, read this tutorial.

Then click on little triangel in the right upper corner.
- Put the .abr file you've downloaded into the folder /Users/{username}/Library/Application Support/Adobe/Adobe Photoshop CS3/Presets/Brushes (on mac OS X) or C:\Program Files\Adobe\Photoshop\Presets\Brushes (on Windows) .
- Then open your Adobe Photoshop, active brush tool, go to option palette and click on to open the brush preset picker.
Then click on little triangel in the right upper corner.