I had this idea for a brush kicking around for years and finally made it. It's great for textural backgrounds, general noise ... you'll find some interesting uses for it, I'm sure! There are 5 variations included - overlap them, resize, try different blend modes, and see what happens.
Photoshop CC: 1) Open Photoshop 2) Double-click the .abr file you downloaded 3) Brushes will appear in your Brushes panel.
Legacy Ps: Select 'Import Brushes' in your Brushes panel dropdown menu (top right corner of panel). Navigate to the file, and select to install.
I don't provide customer support, so if you have any issues, please hunt around online for info on installing Photoshop brushes - very easy to do!
Enjoy the brushes.