Vaginal orgasms are definitely different to clitoral ones - less intense but longer lasting, like muscular ripples that your partner can feel up inside you rather than the strong contractions of clitoral orgasm.
Once I've had one, they sort of come in waves and are very more-ish.
Imho it's about taking the time to get there and finding the positions that work for you, you also need a man who cares about your pleasure.
On top is probably the easiest way of finding your best pace/movement etc. Nice and slow with plenty of grinding against him, multiple stimulation is good too, whether it's having your nipples played with or your bum massaged, when you are not just focussing on one sensation your body kind of takes over and it can tip you over the edge.
The angle of your man can be important too , some of the best orgasms I've had are when DH holds my hips and thrusts upwards and when he comes it can often start me off again with the pulsations.
Experiment with some slow "grinding" and also some hard and fast doggy or your bum up on a pillow, all you really need is a man who can stay the distance, a good 20 minutes + of constant firm stimulation is required, for me anyway . DH has been trying a new technique, squishing my bum cheeks firmly together for 3 or 4 strokes then letting me "drop" onto him, I must say it was very nice!
Basically, don't make orgasm the "main" goal, just enjoy a nice long session, if nothing else it's a damn good work out for your hips and thighs.