It depends which school you are at and which rotations you end up doing. At PUCO we have 4 rotations, and about 1/3 of the class does an internal rotation. We have to do one primary care, one ocular disease, and one specialty/co-management site. The 4th one we can pick from whatever we want, as long as we don't have two of the same type of sites (like two VA's or two private practices).
I have a private practice, a hospital, a pediatric practice and an air force base. I heard that for the hospital site when my attending is on call, I am also on call. Basically it means if he gets called in, I also have to go in. You can't be on call yourself since we aren't licensed yet.
As for what you do, again it will vary based on your site, but you can expect to do anything that you are taught to do in school, state dependent. Mostly you will be doing full exams but some sites will have more medical, more CL, more binocular vision, etc.