Consumable items can be bought repeatedly. i.e. Buy item A (10 coins) twice and get 20 coins.
Consumables are not restorable. i.e. If a user buys a consumable, uninstalls the app, then re-installs the app. The consumable item can be gone (you may do them the favor of tracking it in cloud data, but you don’t have to.)
Non-Consumable items can be bought once and only once. Additionally, you must provide a means for users to ‘restore’ them if they delete the app then reinstall it later.
The concept is simple. You buy a consumable item and that item can be ‘used up’. i.e. Coins, points, etc. Most developer use this as a means of allowing players to buy ‘in-game currency’ in trade for real money. This ‘currency’ is consumed via upgrades, in-game purchase of new items, life-restores, etc.