First off, if you're talking about picking seminar choices online for your first semester, you're probably not going to get your first choice. I listed four or five choices and didn't get any of them; your freshman advisor fills out the rest of your schedule first, then sticks you in a seminar that fits time-wise. Some people get ones they list, but it seemed to me that most did not, so it isn't that important.
As soon as you get your @nd.edu email address, go to ndtoday.com and make an account. All of the teacher evaluations are there, and you can look up different professors. It's a great tool, and it's a great way to pick classes. Otherwise, just put in classes that sound interesting and your advisor will figure it out.
Seminars are largely the same, with the main difference being the subject matter discussed, so that's the only real difference, other than the professor. Good luck with getting a good class.