How do you obtain a student visa?

My question is a little more specific. I am a student at a college in NY and will be doing my co-op (which is a full time internship required for graduation) in London. I have already been chosen as their spring intern. I was looking into information about getting a visa, but it seems that they mostly pertain to people who are studying at a university in London. I will be still a student during this time which is why I was told that I would be under a student visa. I guess what I'm trying to say is that I'm very confused and would love for some legitimate knowledge on this subject. Thank you!