Check out the graphic arts section because some members have posted tutorials on how to make sigs. You can also google it. :3 Most graphics that people have made they use Photoshop, but you can download GIMP which is free and is pretty much like Photoshop. Good luck.
Start with this thread: http://www.kh-vids.net/showthread.php?105571-Gfx-Starter-Guide And look at the other stickys and topics in the graphic section to help you out, like Sabby mentioned.
Like Sabby said, GIMP works. It's free and there are plenty of tuts both on this site or online in general. After downloading it you can decide whether or not you wanna move up to Photoshop.
