Safe word = stop. It doesn't matter which party says it. As the safe word is for ALL parties that are doing the play. Not just the 'sub or 'dom'.
Even if one party says it hurts or they are in pain, it's perfectly acceptable to continue the play.. unless one says said safe word. BDSM is a broad spectrum but it always needs strict consent and procedures prior to play. After care isn't essential but lots of folks prefer it. And a good dom or sadist will always give aftercare. (THOUGH, IT'S NOT ALWAYS THE DOM OR SADIST GIVING AFTER CARE. As dom drops are just as frequent as a sub drop.)
Hopefully this as well as the other comments give you a bit more of an idea of the bdsm world.

It's good but please seun-i don't ever turn blind on your partners pleading to stop next time oki? Cause that look that it hurts