I had something of a scripting background when I first started playing around with plug-ins, but I had never done anything close to the complexity of the C2 plug-ins. Still, I found it was pretty easy to get going, using the methods described by KYATRIC.
I found it was easiest to just start playing around with the edittime.js and runtime.js files, and make very simple changes, to get my head around what parts did what.
In fact, you can just start out with modifying the edittime.js and add conditions and actions, and not even touch the runtime.js file. The conditions and actions you add won't do anything yet, but it will get you familiar with the different components, where they are referenced in the C2 IDE, and how they will look.
As Kyatric said, looking at other plug-ins is also very helpful. I would like to recommend that you look at the OR plug-in, somewhat because I wrote it <img src="smileys/smiley4.gif" border="0" align="middle"> , but mostly because it is really simple. It has one condition, and the logic in the runtime.js is really basic.
Give it a try, I think you'll get hooked once it all makes sense. Good luck!