Asking a question like that with no context of why you are asking it makes it impossible to give an intelligent answer. In general multi player games have a the same mechanics as single player games with the computer replaced by a person.
Sometimes I wonder if you do even the tiniest bit of research before posting... The same way as normal games. There are obviously specific things which certain multi player games can do but are so many types you can't talk generally. The biggest problem for a multi player game is getting the critical mass of players so there are people to play against. Unless you have a big marketing budget this will be harder than you think.