Click one of your units, and then either the place you'd like him to go or the enemy you'd like him to attack. Click the buttons at the top of the screen to switch between units, buildings, and support from the mother ship. To generate units or buildings, or call on support, make sure you have enough credits and that the bar at the top of the screen is green. To build credits, generate miners and station them over the resource piles. Units and buildings can only be generated near other friendly units and buildings.