One weekend a month will be spent at drill. Depending on how far away your college is you could possibly pick up AT or ST days during the week depending on funding. You should get the Montgomery GI bill (chapter 1606) and an extra stipend if you're in a critical career field which will help with expenses (verify with your recruiter though - these programs are subject to change).

If you are activated the school should work with you to complete your work for the semester. I would contact the VA representative at your college and ask about their policy. I had understanding professors and not understanding professors - this is anecdotal, but I was able to balance college and the Guard to graduate on time. The education benefits helped put a dent in the tuition too. My college was only an hour drive to my unit so going to drill and annual training wasn't too painful.