It's not hard, let me point you in the right direction.
Cracking is done through brute-forcing. This is basically just continually guessing the password of accounts. There is a limit to roughly 8 password attempts per account before you are locked out. So the best method is to get a HUGE username list, and a small password list. I normally only use about 3-4 passwords. Then the cracker will attempt to login with the current username and password, and if it succeeds then it will tell you.
I hope that makes sense, it sounds complicated but it's really not.
The two applications you need are:
1.
A username grabber. This collects usernames in-game and should be self-explanatory. Once you've collected the usernames, save them as a .txt file for later use in a cracking application.
2.
A cracker. I believe this is the most recent cracking application. Load the .txt file from the username grabber into this application, enter <8 passwords, and start cracking!
If you have any questions let me know. I promise that it's much easier than it sounds.