Basically, an AB split test is when you take a particular version of what you’re going to test and you just make a different version of it and you only change one individual part.  Let me be more specific to give you a better sense of what I mean.  Let’s say you want to split test an opt-in page and the thing that you want to change is the headline.  So one headline says, Discover the Five Ways to Lose Belly Fat in Ten Weeks and then that you think would be a really good headline but in order for you to know for sure it’s a good headline you want to split test it so the second version is something like, Lose Belly Fat in Only Ten Weeks.  Secrets Finally Revealed or something like that.  That would be version number two so the A version of your split test would be your first headline and the B version is your second.  You leave everything else about your opt-in page the same.  You make no other changes.