All referees affiliated with FIFA have a designated referee level. A list of grade levels managed by US Soccer is given here. Each grade has a recommended assignment level. All referees in Western PA begin as grade 8s. Officiating at a competitive level could be a rewarding experience. As the game evolves, assignors are assigning
Each grade has its different upgrade requirements. The upgrade requirements set by U.S. Soccer can be found here. However, U.S. Soccer expects State Referee Associations to establish requirements that best support the needs of the local competitions. WPA Referee requirements can be found here.
If you want to referee at the professional level you will need to upgrade. Everyone starts getting experience officiating local youth games. Then they continue to work hard and upgrade to the highest level in their state, a Grade 6 State Referee. A State Referee officiates the most competitive matches within the state and region.