Like pro shops at any other golf course, Augusta's is where golfers there to play a round check in. It also includes a modest assortment of equipment and merchandise, including Augusta National and Masters-themed stuff.
During the Masters Tournament, the pro shop is off-limits to fans and anyone else who does not have the proper credentials. (Merchandise tents do appear at other points around the course.)
The "official" online Augusta National pro shop can be accessed via Masters.com, and has three sections - one for prints, posters and photos; one for publications and movies ("movies" in this case meaning official highlight videos/DVDs of Masters past); and one for mobile apps.