The USGA do many many things for golf.
- They are in charge of running some high profile tournaments, such as the US Open and US Amateur. Here they pick the pairings, have full control over course set up (such as tee and pin positions)
- For PGA Tour events and other professional tour events, USGA representatives act as rules officials giving rulings.
- They are incharge of the upkeep of the rules including changes in the rules and trying to make them clearer so everyone can understand and apply them.
- They inspect new clubs, balls and even tees to ensure they conform to their set standards.
- They have rules on Amateur status, which controls the rights and interests of amateur golfers.
The USGA controls USA and Mexico, but the R&A covers the rest of the world. There are two different rule books, The R&A version and USGA version, although they are essentially the same.