I would first say redacted.
(Flutherized answer) If you don’t know how to do that or have any clues, maybe you should wait, or consult a sexologist.
(Actual answer) Taking suggestions on how to ”do it right” is a folie à deux. Having sex is not like running the hurdles or swinging a golf club. The mechanics from one partner to another is different as snowflakes. I could tell you that you have to do this to her Y, and then suck her X this way, then do that half way through. That might work for the last person I was with between the sheets but may not work at all for you to use on your girlfriend. Maybe she doesn’t have much sensitivity from her clit, to tell you to focus on it would be useless. Maybe she would achieve it through stimulation she has never tried yet. Maybe she won’t get the ”mind-blowing” trip to the Big ‘O’ without having a butt plug in place while you are boinking her. The best way is to ask her, and if she don’t know, trial and error. So she don’t get a toe-curling, eye-in-the-back-of-her-head, Jello quaking orgasm the first, second, or third time; when you do it there, it will be special, hopefully.