There is no one 'way' to have F/F sex, and the kind of thing you'll do during a threesome with a man involved will probably differ somewhat from the sex a female-bodied couple would have. You'll really have to just ask her what she likes. A big part of having open, honest, good sex is the ability to talk frankly about it. We can't tell you what she likes or wants, only she can. Lesbians aren't a hivemind, and no two women will have sex in the same way.

Oh and there's nothing 'gross' at all about anyone going down on anyone else. Oh and porn? Porn's got nothing to do with anything. In fact, women who've seen 'lesbian' porn and base their repertoire and way of thinking about sex on that, would certainly not be my choice of partner. Life's not like porn, unless you're a porn star, and porn should never, ever be used as a 'How to' guide, so stay as you are and use instinct and communication.