How pilots communicate with air traffic control.. ?

In aviation, a flight information region (FIR) is a specified region of airspace in which a flight information service and an alerting service (ALRS) are provided. It is the largest regular division of airspace in use in the world today. FIRs have existed since 1947 at least Every portion of the atmosphere belongs to a specific FIR. Smaller countries’ airspace is encompassed by a single FIR; larger countries’ airspace is subdivided into a number of regional FIRs

KLM Cockpit tail series part explanation  :

Always wanted to know what goes on behind the closed cockpit doors where only experienced pilots are allowed? This is your chance – check out the videos of the KLM Cockpit Tales: