Select a mission to play. You have to complete the primary and secondary objectives on a mission before you can unlock the next. Select the weapons most suitable for the mission. You can only carry 3 types of weapon and some may not be available yet. Collect ammo and weapons on each level or buy them from the shop. Use arrows or WASD to move your helicopter, mouse to shoot, space to winch up or down, 1, 2, 3 to toggle weapon.