Hey there!
In that topic I'm gonna give you a little introduction into the use of Brushes. That guide is for Photoshop users only (sorry GIMP's).
Lets start with getting the brushes. Some advertise for me: Check some of these out:
Download: Click
here - Click on 'Download', then click on the left side of the page on 'Download' again.
Installation: Extract the .rar Archive into the folder:
C:/ ... Adobe / Photoshop / Presets / Brushes / folder and open your Photoshop. Select the Brush Tool and click at the top this arrow

Now click that symbol

and select 'Load Brush'. Select the extracted .abr file. That's it.
Tutorial: If you want to create images like the preview images I've posted, then check out this tutorial:

I hope that little introduction helps you ;)
PS: Other great brushes you will find here:
Click meIt's the greatest source for stuff like brushes.