This is a huge subject.
A very few girls advertise as subs. Last week I met with one who does, for the second time. She certainly knew what was expected of her as, she volunteered, she had been well trained at the age of 18 by an older master. They were in a sub/dom relationship. We spent some time on impact play; spanking, flogger and riding crop. To gauge the appropriate level of impact, I would ask her to rate each stroke out of 10 for pain. We got to 9.
She remained blindfolded, cuffed and had her nipples clamped throughout. I also kept up a narrative of what I would do to her, what my requirements were etc. This treatment got her very wet, as I discovered on checking her. After extensive use of increasingly large butt plugs, we ended with anal.
She clearly enjoyed it all as much as I did. She admitted to having been a Fetlife member before, but has a better time with guys she meets on AW with, as she says, no strings attached.
Such girls are the exception. I have, however, had very satisfactory experiences with four others who did not build their profiles around BDSM but who, it turned out, liked it anyway. It has been mentioned in other posts, that some WGs, bored with a constant diet of vanilla, actually get off on some spanking and submission.
I would advise any newbie that some subs are more into being submissive and wanting to please their dom, rather than being into the enjoyment of pain itself, although some are.
So, go easy at first and take your cue from your sub. You want to hurt her, but never harm her.