This is an example of what all GLO's call doing your research first before you post... It is clearly obvious, you have not done it.
Search on GC and Google as a START it -- is your friend.
Find the answer to this question: What is the RUSH system? That can easily be found here, on your college's website and the National Panhellenic Conference's website, and all associated affiliate organizations.
I am unclear of any sorority by the name of "aha"... "Alpha Eta Alpha"???
Good luck!
ETA: Going to college and getting an education needs to be your first priority before you think of joining any extracurricular activities... Congrats on your acceptance, but seriously, as easily as you got accepted, you can be easily kicked out if you are unable to manage your coursework. If I have seen it once, I've seen it a million times...