when you see a patch without + or - it's because the author creates a new class.
example,if you see in a code without + or - this:
package com.l2jserver.gameserver.datatables;
you 'll understand that you will have to create a new class in this specific package,now about the name you'll just have to see what's the name of the class,here:
public class PvPRewardsTable
so PvPRewardsTable will be the name of the class.
in order to create a class,you'll have to right click -> new -> class.
about the 2nd part of your question,just read some tuts/guides in the forum [use search button and you'll be k]