briefly---
start training..45hrs in air flight training and pass 4 written exams (air law - met - aircraft general - flight performance & planning) sit a flight test and you have your ppl (private pilots licence).. within your training there will be certain requirments that must be met before you are eligable to sit the flight test.. such as min amount of "p1" pilot in command, and solo hours, long navigation with diversions tryangular eoutings of over 150nm (150 nauticle miles) and a few other bits and pieces.... all no problems.
after your ppl comes your cpl (commercial pilots licence) 7 written exams and again min amount of hours must be flown anong with some other requirments such as instrument time, and certain specified navigation exercises.
after your cpl comes your atpl (airline transport pilots licence)-- YOU NEED THIS TO FLY PASSENGER JETS. 14 exams, similar to cpl with much more detail and alot more work.
On reaching the min amt of hrs, passing the 14 exams and passing the flight test you will be issued with a frozen atpl... which will rthen soon become un-frozen when you are offered a JOB AS A 1ST OFFICER WITH AN AIRLINE. In addition to your atpl you will also need an instrument rating and a mcc (multi crew co-operation cert) and a crm (crew resource management cert) although they are not a legal requirement.. all airlines require them.
thats it....... ion its simplest form... (very brief)