When you begin, take out all the guards leading up to the two Ghille snipers and jump on the bottom car on the stack next to the two guards that where talking. After you get on the first car, jump and you should get on to the second. That part is fairly easy; if you cannot get up, you are trying it on the wrong cars. Once you are in the second car, stay on the hood and do not get on the roof. There should be more cars to the right when you get up. Jump onto the hood of those, then jump onto the large metal crate. Next, jump onto the roof of the cars that were behind the cars that you where just on. Once there, jump through the top of the bush and you should be out of the level boundary. Do not be afraid of the clear ground. Walk over it and more ground will appear.