How to? - Adding for testing purposes

In this post, Mason spoke of adding email addresses for testing purposes but I don't understand how to do that.

"For my own, I use the +1 method. You can do this with gmail addresses (and many others) so:

You can really do + anything though, so you could do email+level1membership, etc.

Works pretty well and has the advantage of providing you with the ability to actually receive the email notifications and such."

Is there a tutorial or can someone provide instruction?

Thanks so much for your help.