How do PPL, CPL, and ATPL compare?
PPL is Private Pilot License

May fly for pleasure or personal business. Private pilots cannot be paid, compensated to fly, or hired by any operator.

CPL is Commercial Pilot License

Can be paid, compensated to fly, or hired by operators and are required to have higher training standards than private or sport pilots.

ATPL is Airline Transport Pilot License

ATPs, as they are called, typically qualify to fly the major airliners. ATPs must qualify with a range of experience and training to be considered for this certificate.
— Wikipedia