The Arsenal has several useful items that will help you aid you during your mission.
You can get more items for your Arsenal by using your credits.
How to use the Arsenal
From the map, find the Arsenal icon on the middle-bottom of the screen.
Tap and drag to equip items to your Arsenal. You can only have three at a time.
Once equipped, you can tap and drag another item over a previously equipped item to replace it.
The number over the items will show you how many each you have.
If you wish to purchase more, tap the item to do so.