Compared to a public game of TFC, where any player can join in and do pretty much anything they like, a clan match is a very organised affair, with clear roles for every player and even referees spectating to ensure fair play. Most clans compete in organised leagues and tournaments around the world, playing scheduled matches against other clans in competition for prizes or simply the honour of winning. Clans often use voice communication software, so that they can speak to each other during a game and co-ordinate their actions. It's a very strange experience to be able to talk to the people you are looking at on your screen, but it's unbelievably helpful in a game. Imagine being able to tell everyone where the flag was dropped, rather than have to type it all out.
Many clans own or rent game servers, which they practice or play games on.
When not in use, they often open these servers to the public, providing a place for anyone to have a game. The advantage of having your own server is that you can choose who plays on it, which maps are played, and you have total control over everything else that happens there. The best way to join a clan is to be invited. If you play exceedingly well in a public game, a recruiting clan player may ask you for your contact details. Most people consider it slightly irritating when people continually ask if any clans are recruiting or if anyone wants to join their clan on a public server.