Pick up weapons and upgrades being dropped by your allies.
Helicopters come at you in waves, your mission is to take as many choppers down as possible.
The real-time strategy genre as we know it today--gathering resources, building bases, and massing huge armies to sweep your opponent from the map--owes a lot to Command & Conquer. The original Command & Conquer was one of the first true real-time strategy games, as well as one of the best games ever made.