Forget about the average lap time, that will be automatic when you finish a race.
The fastest overall will have the fastest average lap time and so on down the list.
The results are calculated on the car that covers the most distance in the time allowed for the race,
eg 5 minutes plus seconds required to finish the lap it is on.
example 15laps in 5min 12.325 secs
This is the result that race control look at for qualifying and race finishing positions.
Your average lap time is worked out from this result.
Your consistancy is one of the things that a lot people don't look at, the lower the better, but that doesn't aways win you races.
Farstest lap means you got your act together for 1 lap (or may have even cut a corner if too fast)

Now I hope that is clear as mud