There are little differences, but you need to look at FAA in the USA or JAA in most other parts of the world.
There is a CPL (Commercial Pilots Licence) and ATPL (Airline Transport Pilots Licence).
To get the CPL, which is what you get before ATPL you need.
- PPL (45hrs + 6 exams + C2 Medical)
- 200 hours + (100 must be PIC "Pilot in command")
- IR (10HRS +)
- 14 JAA/FAA ground exams
- C1 Medical if you have the C2
- 300NM flight with 2+ full landings
- 5hrs night
- 30hrs x-country
(£30-60k depending on if you do modular "part time, stages" or integrated "full time, 0-cpl")
Then you can take you CPL skills test. At this point some have already done MEP Multi Engine and MCC.
At this point you have a CPL, that means you can fly for pay, but not fly command in a transport aircraft.
CPL pilot can land on their feet and get an airline to give them a type rating, and then they can fly as a 2nd officer until they get 1200 hours. Untill this they have a frozen ATPL. Once they get 1200 hours+ depending on where the hours are spent, they get a full ATPL, and thus a 1st officer.
If you don't land on your feet, CPL's usually use there frozen ATPL to be a flight instructor, which you need to do an FI course, some will self sponsor a type rating at a cost of around £20-30k and then you can hunt for a 2nd officer job. You too could use your cpl for many other things, dropping parachuters, arial photography, etc.
I have the best part of 10 pilot friends, and know many, many more via the internet, and most don't have degrees, most are in mid 30's, most have saved up since early 20's to fund this as you are looking at 60k minimum when you factor in a years lost work where you will need to still feed family, etc and fees, tests, hours, certs, retakes, equipement, etc.