RDA first zone.
At the start of this zone you will control a Scorpion, which is a helicopter-like flying machine, and you must destroy 5 Banshee nests. They are in the mountains and there are a lot more than five. Be careful of the acid firing plants, they are green and are easily avoidable.
At the end of this zone you must enter a cave infested with Viperwolves and Na'vi warriors. You must grab the crystals and escape. This is a fairly easy mission, just don't be afraid to use your skills as they are vital to your survival.