This game is very similar to the classic Missile Command game. The hostile missiles are coming in from all directions and you have to shoot them down before they reach your bases.

Use your mouse to aim and fire your scud missiles so that the explosion will destroy the incoming missiles.
You have a limited number of mega-scud missiles that travel faster and have a large explosion. Launch a mega-scud missile by holding the space bar when you click to launch a missile. Each level you will earn a mega-scud for each intact base you have.
Between levels you will have the opportunity to repair your bases before the next attack.