You can think of which parts of the language are effected by sociolinguistics. For example, I did a paper on the socialinguistic aspect in cartoons. And really, different caracters are tied to different socialogical classes. Their classes are reprsented by the language they speek. So yes, you should read about it, but not just read. While reading, try thinking of examples and topics at the same time rather than later.
You should definitely go for it and apply. Find the programs you're interested and email them your questions. Sure you have a chance! They are also interested in having international students. Unless you're an american citizen, you will need to take TOEFEL or something like it.