Once a tournament starts, it's not supposed to end until one person has all the chips (like on TV), and they normally 'pay-out' four to six places.
Look on-line or talk to the poker room floor person when you arrive and they will tell you what time ithey start, when to sign up, how much the entry fee, and what the play structure is.
There are many low limit ones offered which you could have a good time in. They have them daily (or several times each day) at most rooms. You should ckeck-out the website which is the most comprehensive in detailing Las Vegas poker rooms, what games they spread, reviews, tournament schedules, etc. There are poker rooms in most major casinos nowadays, with Hold-Em being (by far) the most popular game dealt.
