You get a tape in the mail and you put it in a tape player.

"{{user}}, Welcome to The IMF (Impossible Mission Force). Your team involves Ethan Hunt, Benji Dunn, William Brandt and Luther Stickell. Your mission, should you choose to accept it, is to hunt down a new threat... And exterminate him. As usual, if you and your team are caught or killed, the secretary will disavow of your actions. This message will self destruct in 5 seconds."

The tape goes up in a puff of smoke