ATC Community Manager for Infinite Flight, Tyler Shelton on the definition of an ATC operation in Infinite Flight:
An operation is counted for each clearance issued. This includes tower takeoff and landing clearances along with approach clearances for the ILS and GPS which are worth more operations. A user can also gain an operation for aircraft serviced with radar vectors or flight following while working a radar facility.
You’ll find it most fun when you don’t count your operations daily, or weekly, or monthly, ect. but it’s good to know. Quality over quantity!