some big problems.........

hi i am making a car racing game and i need help from you.The problems are
:-how do i count points and how do i use it to activate the finish line so that when a player have collected the given then he allowed to go in the next level

:-the other (big) problem is that i don"t know how to make opponents for this game
if any one know how to do solved these problems please help me.

and you could try to make something similar for the checkpoints