Can someone answer a few questions about Sororities?

Please, no rude responses bashing sororities. I start college this fall at Ohio State University. I'm extremely excited for Greek Life, and I've researched each house individually. I have a few favorites on my list, but I'm not positive which I'd like to join, obviously because I haven't even started college yet and only know what I've read on the internet. So, my question is, how does rushing and pledging work? I mean, is there like open houses that I just go and visit each house and see what the girls are like? Or do I just choose one? Do I have to be invited before I can rush, or is it open up until the point of pledging? Also, do they accept freshmen? I really don't understand the process. All I've seen about it is on TV, and that's never a reliable source. Any help is appreciated!