The ATPL that you are talking of is the theory element of the Commercial Pilot's Licence.
Here is the process to getting the full ATPL:
1. You get your PPL.
2. Complete ATPL Theory course (100% theory).
3. Do CPL flying instruction and CPL practical test.
4. Do Instrument Rating flying instruction and practical test.
Then you have what's called a Frozen ATPL. It becomes a full unfrozen ATPL when certain multi-crew flying hours are completed.
Of course there is far more to it than that, including hour-building to qualify for some of the experience levels, but you have the basic idea now...
So yes, the ATPL as you mean it is the theory course. It takes a minimum of about 9 months part-time study but frequently takes longer.