The other thing to note, aside from what earlier posters have quite accurately said, is that you apply to the university, not the course. Whereas in England you choose 5 courses (all of which could be at the same uni, if you wanted), you don't apply to US universities with a subject in mind. This is why they place so much emphasis on extracurriculars - because you'll be getting a broad education, with classes in multiple subjects, even ones that aren't related to your degree, they don't really care about how good a Psychology student you are. They want to know how good a student you are full stop. It's all about being rounded, not being specialised. It's virtually irrelevant that you want to study Psychology, which is why they don't list minimum grades. It's a four year course, so not until the third/fourth year will you start to specialise and choose your major. The first two years are much broader in the liberal arts.
Seriously, look on the Fulbright website. It has a huge amount of information, just read it through carefully. The process and requirements are nothing like in the UK.