I recently started college and there are quite a few attractive girls I have seen around.

In class I usually sit alone and almost always a different girl comes and sits next to me. I have no problem asking their name, making small talk and making them laugh, however nothing comes from it and I usually never see them again (there's usually a few hundred in the class at once). How can I escalate further and make a connection with these girls and potentially move to a friendship/relationship?