How can i read defenses? like when theyre going to blitz ?

You have to know the tendencies of the defense you are playing. That's why QB's and coaches spend hours upon hours watching game tape. You have to look at what the LB's and Safties are doing, and what that they usually do from there. Like if they are moving up it might mean they are rushing or it might mean they are picking somebody up. The only way to know is if you study game tape because they might be faking and moving up just to drop back in a zone coverage.