In my day it was largely from magazines like Just 17, and Cosmo. And a certain amount from films and shows like Friends. Not the best of sources and there was a lot of sorting out reality from fiction.
There are often posts on here with young women questioning things that have happened during sex, that my generation (I think) were quite clear crossed a line. As much as Cosmo was pushing heavily for acceptance of anal sex, they were pretty clear on the concept of consent.
I know that porn seems to be the main way that men learn about sex, but I’ve been wondering about the younger women and today’s teenagers. Particularly as I have a tween dd and I’m horrified at the idea that she might absorb these ideas that she owes men hardcore sex experiences.