You need an Amateur Operators Certificate of Proficiency to operate on Amateur radio frequencies unless you are directly supervised by someone else who is so qualified. Once you've passed the exams, the qualification remains with you for life. There are some acceptable alternative qualifications, mostly overseas amateur radio licence exams or professional technical qualifications.
You need to licence your station if you own your own Amateur radio equipment and wish to use it. You won't get a licence for the station if you don't have an appropriate certificate of proficiency. The station licence is renewed annually.
I currently own several old Amateur band radios. My station licence lapsed many years ago, but my certificate of proficiency remains valid. I cannot operate my own radios at home, but I can operate any amateur radios at someone else's licensed station, using their station's call sign.
Neither an Amateur station licence nor an Amateur operators certificate of proficiency permits you to operate on an air band frequency, a marine radio frequency, nor the local taxi company's frequency, even if your Amateur radio gear is able to transmit on frequencies allocated to those services.