Being such a unique game theory of tower defense played as a FPS with resource management, this video should help explain how to play successfully. It ain't easy!
Level 1 is meant to be a tutorial to help you learn how to play the game. The game is intentionally quite challenging, making you plan wisely, react to changes and punishing mistakes.
The battlefield of the future is looking more like robotics vs robotics and this game may be a vision of things to come.