Call, e-mail, stop by. The best would be calling and stopping by. E-mail takes them forever to respond.
To document: either use the provided forms on your university's website, if required. Some universities require you to use THEIR documentation rather than the one you make. But if you're using one you made yourself, then I would recommend recording the date, time-in/time-out/# of hours that day. You should get it signed. Either by each time, or at the end.
I made my own and used it. Here it is to give you an idea (attached).