Creating Custom Brushes
Open/create the image you want to be a brush! I will use THIS; for a better outcome i recommend making in transparent.
Click the paint brush tool, use the drop down and you should see a little brush. Click on the square all the way at the bottom right corner.
A new window should appear and you just click OK if you see your brush on the preview; should look something like THIS.
That's it, you have created your own custom brush. =)