If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
This is a classical aircraft top-view shooting game. You're flying forward in your aircraft and need to destroy the enemies you meet and try and avoid their bullets. There are quite many different enemies in this game and each one has its unique behavior that affects its movement and the way it shoots.
W,A,S,D / Arrow Keys - Move.
Spacebar / Shift - Shoot.
1-3 - Change Weapon.