Are the showers private with curtains and things like that?

Yes, there are curtains or doors on the showers

My friend who went last year to Philly said that it's a good idea to wear flip flops in the shower?

Yeah, the showers are used by a lot of people. I didn't personally wear flip flops; the thought never crossed my mind, but I think a lot of people do. It's kind of a hygiene thing. When you go to college, you'll definitely wear flip flops in the shower

so there is only one shower/bathroom for every floor level in all the cities? or are there some that are different? (I'm going to LA session 3)

I think that most of the dorms have 1 bathroom per floor or wing depending on how big the dorm is. The bathroom will have a few toilet stalls, a few sinks, and a few shower stalls

after we shower, where do we go to change/wear our clothes??

That's up to you. A lot of people just wrap a towel around them and walk back to their rooms. Some move over to toilet stalls to change. Some change in the showers

Okay, quick question, we, my mother and I both, looked around and couldn't find anything about towels. Do we need our own personal towels or will we be provided with towels there?

They provide you with one set, I believe. You may want to bring an additional set with you though

Thank you very much for the info. ^-^