Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Well I've read the intro thread in tournaments but I'm still not 100% sure what type a tournament is, like what tournament is type A and what is type B etc..
Well.
Type A are as standard as it gets.
Type B are standard but there are usually some rules that alter the games. Example: X or Y pokemon are banned, obligation to use X or Y item, X or Y types are banned/forced to be used. You will find the same strategies as in standard plays but you will have more/less limitations in what you can use.