Click to see the factory menu, again to purchase one, and then again to place it behind your wall. The arrows coming out of the factory as you place it indicate where roads can be built. A factorys roads must be able to connect to the main road for the factory to go into operation.
Watch the weather forecast. Factories that use smoke will work slower in the rain, and conductive robots can be destroyed by lightning.
As you play and defeat enemies, new factories will become available.
Click a factory to view its upgrade options, or to sell it.
Click HP to buy health for your wall. Click EMP to release an EMP blast that will destroy all nearby robots (including your own).
Build an army of robots that will reach the other end of the battlefield, exploding on impact with the enemy wall. Take down the enemy wall without letting the enemy take down your wall.