what does the I and L positions do....L is for lower???....does it make are car faster comming out from one of these positions?

 

Halfcent did a great Automatic transmission launching guide. L for low is basically '1st' gear as I have read around here. It will take off traction control which is why it is good for the brake launching. I stands for intermediate. It does not use the overdrive gear so it will only go to 3rd. If you don't want the car shifting so much, you can put it in this gear (it will not shif until the engine has gone to 3500RPMS and it only shifts there). If you are going down a hill, you can put it in this gear for engine braking. The wheels will spin the engine, slowing the car down depending on how steep the hill is. IMO, this gear is useless if you are not using the brake launch because it has worse fuel economy than Automatic Overdrive or 'D'.

EDIT: This is Halfcent's guide on Brake Starting.

 

Also, when you put it in L, the car will shift to second when the tac redlines.

I disagree with the previous statment that I is useless. It would be great for hilly terrain and would stop the trans form constantly shifting. i also use I when we get lots of snow, lets the car use the traction control and also uses the engine to brake.