You can place custom brushes in this folder, and SpeedyPainter will automatically load them at application startup.
A valid brush is just a png image, with trasparent background, and where the only colour used is black (with different opacities in different areas of the image).

This video demo shows how create a custom brush:
http://www.youtube.com/watch?v=yfMDLebMwug

As an alternative, you can also copy here brush sets in the common Photoshop(R) .abr file format. SpeedyPainter will automatically load them at startup.