You can start by saying... "
My name is X, and I am writing this letter
because I saw your advertisement posted on a well-known scholar site
about these classes that instantly drew my attention. For that, I would
like to ask if you could give me an input about who is running the classes,
whether the instructors are qualified, and the place where the classes will be
You may end with a polite closure, like: I am looking forward to seeing your reply, X "