If you need to know how to install them go here:
After installing them, apply them to your graphic, and add some blending options. Have a play about with it, to see what fits the image best.
Basically get the files, go to the Photoshop directory and look for "Presets", and just copy the files into the brushes folder. Restart PS and after clicking the brush tool, where you select what brush you would like, it should have the name of your set of brushes. Click on it and Voila