How do I privately sign my applet?

I have a dinky little applet that needs a signature because it needs to access the clipboard but I have no real desire to shell out crazy money for a hopelessly amateur program that I wrote just to teach myself Java to get a real signature.

All I have are the class files currently, and the applet works 99% with the 1% being the clipboard function that doesn't work. I think I need to get these files into a jar and then use jarsigner but I can't even seem to get jar to work, much less what the hell I should be doing with jarsigner. If anyone can post a step by step complete idiot guide to signing an applet it would be much appreciated.