Nether Earth was the very first real time strategy game. It worked on a SPECTRUM machine, and only needed 48KB of RAM to work!! It has all the tipical elements of strategy games: resources, factories, combat units, etc.
As in almost all strategy games, the goal is to eliminate the enemy. To achieve it, you have WARBASES, that have the ability to produce ROBOTS (your combat units). You can design your own robots by combining several pieces (TRACKS, ANTIGRAVITATIONAL DEVICE, CANNONS, MISSILE BAYS, etc). To build robots you need RESOURCE points. Each warbase procudes 5 resource points every day, but you can increase it by conquering FACTORIES. To conquer a factory, let a robot stay in its door for almost 12 hours, then the factory will be yours. Once you have a combat foe ready to attack, you can send your robots against the enemy robots, factories or warbases. To conquer a warbase you have to follow the same procedure as to conquer a factory. Once you have conquered all the warbases, you have won the game. Will you be albe to conquer all them?