Natural ways to induce

Okay so this might sound dumb but I really do not know. I keep seeing people say that sex can help induce labor or at least help prepare, so my question is what about sex helps will masturbation do the same clitoral or penetrative is it the sperm and is there certain positions? And with nipple stimulation how does that work I don’t have a pump, tmi but is it the same if SO sucks on them or do you rub them I’m a bit lost 😨