I see a few issues here, but they're all solvable. Certainly this is an important rotation for you.
1. If you have the time to review the charting and EHR practices of this hospital, do it. You can innocently find out what EHR your hospital will use, or inquire as to if they'll require a training to give you access to it. More than likely there won't be a lot of physical chart work, but that's still very hospital-dependent. If you get an idea of the EHR and what it'll look like, you'll be fine.
2. I would just scan the threads of SDN to find out some info about the daily life of gen surg residents. They honestly don't differ immensely between institutions. It will be expected at first that you won't know everything about how the day works. In general there's pre-rounding/rounding, some AM conference, OR throughout the day, and occasional PM lectures. But this is totally hospital-dependent and they'll teach you that.
3. Will they tell you what specific services you'll be on? I wouldn't go overboard studying, but I would make a point to review the surgical anatomy of those fields. If you get assigned to breast, you should have a basic idea of the breast anatomy. If you're on a service with a lot of scopes, watch some videos and look over the anatomy. Most attendings know that you won't necessarily get most of the basic technique at first, but they do expect at least a loose grasp of the anatomy.
4. When you're on rotation as a medical student, your role is somewhat limited. You won't be the focus of the attendings - they're trying to help patients and train residents. Residents will have a major role, and often medical students can't do many of the jobs the residents are assigned to. However, my best medical students figured out how to do the little things. They got consent forms and pre-filled them out when I saw a consult that was operative. They got me splint/ED supplies so I could do bedside procedures. They rapidly learned how to do basic procedures like drain removal, suture/staple removal, and bedside vac changes. In the OR, 75% of your role will be retracting and holding. That's a somewhat boring but nonetheless critical job. Watch where the attending/resident go and try to move the retractor to help. When they get instruments that usually have some sort of cleanup/suction/bovie/cutting second step, make sure you're ready for it. Be respectful to the scrub nurse, and see if they'll let you ask politely for a suture scissor or army/navy retractor. If it doesn't work, that's your limit, so don't keep trying to overstep it. Eventually maybe you'll get that requisite level of trust.
I hope this helps. In short, know anatomy, watch closely, be quiet and listen, and be friendly/warm/respectful. If the program's a fit, they'll love you. If it's not, sometimes it's simply not a program culture match, and that's ok too so long as you worked your hardest.
