There are many way for them to have sex. one is just to kiss each other and rub their vagin* but that is only one way. another way is for you to open your legs and the other girl suck on it (between your legs). Another way is for both of you to open your legs and press your vagin*'s together and rub against each other
Lesbians do it in many forms. There are toys you can insert (vibrators, d*ldos, etc), using their fingers, "scissoring," which is pretty much placing one leg over one girl's leg, and the other one underneath the opposite leg, and grinding their "lady parts" together, and there's also oral play.