The Marriott Rewards Program has been combined with the SPG Program to become one program. You can get all the details of the combined Marriott/SPG Program here.
As a member of the Marriott Rewards program, you can EARN Marriott Rewards points. You can then USE these points for free travel. As a member of the program, you also have the opportunity to gain Marriott Rewards Elite Status by paying for stays at Marriott Resorts (or Ritz Carlton resorts) or by using a Marriott Rewards Premier Credit Card. Elite status offers additional membership perks and benefits.
Marriott has numerous hotel brands with locations worldwide. Marriott divides its hotels into ascending tiers, in their case nine, with the more budget-friendly, full-service hotels in the lower tiers and the top-shelf luxury hotels in the upper tiers. The Hotel Tier determines the number of points required for a complimentary night.