"Customize" is a selection screen in Star Warfare where you can edit and rearrange your load-out for weapons, armor, and items that you have bought in the store. It can be accessed in-game by tapping the 'Customize' icon in the pop-up menu by tapping on your rank.
Armor, Backpacks, and weapons can be customized by switching to the armor/weapon/backpack of choice and clicking the 'equip' icon below the item description. Please note that any item a player wishes to equip must be purchased before it is rendered visible in the customize screen.
Weapons, items, and health-packs which the player desires to bring into battle must be selected in the 'Pack' icon at the left-hand side of the customize screen. Once inside, there will be a set of grids up top - weapons/items/heath-packs already owned - and a set of grids at the bottom, those which the player wants to equip into their backpack. To equip any item or weapon, simply drag the icon from the top grids down into the backpack slots.
Weapons can also be upgraded in the customize screen; higher levels will increase the damage a weapon inflicts. This can be done by tapping the 'upgrade' icon in the weapon's description. Each weapon can be upgraded 8 times, with each upgrade raising the price for the next level. The costs for each of these upgrades can be found in the weapons upgrades list.