not sure which one you're interested in but talk to those you know that are in that sorority of interest. ask them about their organization and what their upcoming events are. i would then go to that particular sorority's website and read what they look for in a candidate. secondly while online, see if that chapter has a website and see what it's about. each of the four has a page on this site, go there for advice. not by asking tons of questions, but by reading.
start doing your research. we've done it, so can you.
good luck