Revives are items that allows Trainer to restore health of fainted Pokémon. It works only on Pokémon that HP is equal 0. They can be acquired from leveling up, spinning the Photo Disc at a Gym or PokéStop, or defeating a Raid Boss.
There are currently only two types of revives:
and Max Revive.
To see currently owned Potions player can check them out on the item bag page
Revives can be used quite similar as potions at any time during gameplay. They can be found on the item bag page. After taping on revive, list of fainted Pokémon with 0 HP will appear. Tap the desired Pokémon to use the item on it.