Question about sex scenes in movies...

What do they do when there are two people to are both completely naked and clearly grinding genitals? Is there some sort of patch over their genitals, or are they actually making physical contact in that area?

Is there anything they do to keep the male actor from getting an erection? I imagine that’d be hard to avoid considering they’re steamy scenes with beautiful women.

I’m just really curious about the overall logistics of how they do this stuff while maintaining an overall comfort level between the two actors.