fraternity spring rush

I’m going to be a freshman in the fall and, while I want to join a fraternity, I need to focus on my grades my first semester. I heard that some frats do spring rush and was wondering how big it is/how to do it and which ones usually allow it. Also, I was wondering if it would be hard to rush as a sophomore if I didn’t do spring rush. My sister went to ole miss and I know it’s hard for girls but she doesn’t really know anything about fraternity rush.