I, for one, will freely admit that I didn't really know until after my divorce.
I had very little in the way of sexual education at school (an all boys school. All that happened was lots of noise from the boys, trying to show off.. I didn't really learn anything)
After that, I kind of made it up as I went along. Nobody took the time to show me, or tell me what they wanted, or what I "should" be doing - I never really got any feedback from my partners (including my XW) about how /what I was doing, so just assumed everything was fine and dandy.
After a particularly bad episode, I took it upon myself to try and get educated about the female body. I struggled. Yes there are lots of diagrams and pictures available, but they aren't much help when it's dark, and you are fumbling around. Also, asking someone if it's ok to compare their "bits" to a picture on your phone tends to be a bit of a passion killer.
After my divorce, I was extraordinarily fortunate to have an open and honest relationship with a woman, that I could admit all this to, and who was willing to take the time to help me discover her body.
It made our sexual relationship fantastic.
Ladies, don't assume your man knows what he is doing, or where everything is. He may not. Don't be afraid to guide or even show him. You may both be grateful for it!
Guys, don't be afraid to own up that you don't know or understand something. It doesn't make you any less of a man.