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.
Starwood Hotels & Resorts include brands Sheraton, Westin, Four Points by Sheraton, W Hotels, St. Regis, The Luxury Collection, Le Méridien , Element, Aloft and Tribute and are located all over the world. Starwood divides its hotels into ascending tiers, in their case seven, with the more budget-friendly, full-service hotels in Categories 1 and 2 and the top-shelf luxury hotels in Category 7.
Starwood merged with Marriott back in 2016. You can read here about the merger and how it currently impacts your SPG account.