L2J Server

Very often when I read someone's contributions it's set up as a differences like...

+this info
-that info

how do I make that kinda of thing so that I can share my contributions in this manner as well... is this a program?

yes it's a program called Eclipse, with a plug-in called subclipse.
there's a wiki page all about it:

http://www.l2jserver.com/trac/wiki/Eclipse

once you have everything installed, you need to right click the modified file\folder, and do:
Team - > Create Patch
then you can either save it to a file, or it copies it to clipboard so you can paste it in websites like
http://www.pastebin.cz
or here on forum using the "