Zombiewood Hints for iPhone/iPad
Also on: Android
Use the coin currency you loot from zombie corpses to upgrade any weapon you own by returning to the shop and selecting the 'Upgrade' option and increasing damage, ammo size and firing rates.
To make progress through the game you must successfully complete the reels. If you need to top up your total you can always return into earlier levels and try to master some of the objectives. Doing this will also earn you currency and XP.