Quick tutorial to install ProBrush™ brushes for Adobe Illustrator
Windows users: You need to open them from Illustrator:
Brushes - Other Library - find brushes and just click on them.
Mac users: Just copy all of the brush files into your Illustrator brush Library.
(User - Library - Application Support - Adobe - Adobe Illustrator (your version) - Your Language - Brushes)
I hope that was helpful!
If you have any questions be free to contact me!