A brothel is a place where people, usually men, pay money to spend time with women (or sometimes men) who offer sexual services. It's kind of like a store where you can buy a special service like getting your hair cut or your nails polished, but instead of haircuts or nail polish, people buy the opportunity to have sex.
It's important to know that going to a brothel is not legal in all places. In places where it is legal, there are certain laws and regulations that the brothel and the people working there have to follow to make sure everything is safe and consensual.