In Sky War, you're flying at the enemy planes but you're not at all equipped to take them down: you've not been issued any guns or even shields! Every now and then a booster icon will appear. Grab it to gain weapons and defenses so you can take down your opponents. Watch out, because every booster is temporary and won't last for long. Do what you can, and then zigzag past your enemies to pick up new booster icons.