Flight pay is generally based upon the moment the aircraft moves under its own power until that point where you set the brakes at the arrival gate. Some companies will have your pay start when you release the parking brake for pushback, it all depends upon what's agreed to in the contract.
You will usually be paid your minimum guarantee or whatever block hours that you've flown for the month, whichever is greater. The times can be kept automatically if you have ACARS. If your airline is too cheapskate to have ACARS installed, you'll call your times in to the ops guys.
Not all airlines do it all exactly the same way, but generally it works this way.
Southwest Airlines pays its pilots by the "trip." Each flight segment is assigned a value in hourly pay, and the actual time needed to accomplish the segment is ignored in pay calculation.
I would invite Southwest pilots to chime in on exceptions.
Southwest is unusual in this respect. The vast majority of airlines pay "block" as the previous poster mentioned.
Many pilot unions have negotiated certain pay rules that make things more complicated, but for the most part you are only paid when the airplane is away from the gate.
So in direct answer to your question, you are not paid for the preflight inspection, weather checking, etc. as such.
Cant tell you on airlines because I don't know any that work on that basis.
In the smaller aircraft it works on flight time. You do get SNT aswell, meaning you sleep away from home you get paid more. Also a lot of companys work on a mile basis, so you get paid by the mile you fly.