Note 2: This is about completing the race.

0 = Normal race. Complete the race by racing through the checkpoints, kill the peds, or waste opponents.
1 = Cars. Complete the race by wasting all of the opponents, or some of the opponents. Replace the "laps"-line with the following:
2	  // Number of opponents that must be killed (if one, only one line follows this line, etc.)
0	  // Opponent "0" (Red Eagle) must be killed
4	  // Opponent "4" (Lady Bug) must be killed

2 = Peds. Complete the race by killing peds only. Now replace the "laps"-line with the following:
1	// Number of ped groups (-1 means all)
42	// Group number (Data/peds/settings.txt)

3 = Checkpoints. Complete the race by racing. Now you can keep the "laps"-line, and write the desired lap count.
4 = Destroy objects. (For example oil wells, carrier weapons system, roof-top satellite antennae, etc) Replace the "laps"-line with the following:
1	// Smash variable number, seems to be always "1".
11	// Smash variable target, the number of objects-to-be-smashed.
See "Other smashable stuff"-title to learn to define, what smashable objects count as mission targets. (What you have to destroy to complete the race)
5 = Destroy objects & kill peds. (Carrier mission) Again, replace the "laps"-line with following:
1					// Smash variable number
19					// Smash variable target
56					// Ped group index for required extra kills