Yes, you have to join Marriott Rewards before you can start earning points. And yes Marriott does have some bonus point promos (Megabonus). Marriott also has other promotions as well like Bonus Bucks (BB) and Premium Pounds (PP).

I would suggest you spend a little bit of time searching through some of the various threads in this forum to learn a bit about Marriott Rewards. As you learn, if you have specific questions then you can post either to an existing thread with a matching topic to yours or you can start a new thread if you can't find a comperable topic.

Some good threads to start with:

Marriott newbie questions....
Fall 2007 Megabonus Finally Here!
Question about Marriot Points vs Airline Miles...
Which reward program is better, Marriott or starwood??