Soul Chalices are rare items, very useful for buffing you during combat.
Soul Chalices can be found in chests in Bastion Remnants and Ancient Cities.
If you kill a mob with a Soul Chalice in your mainhand or offhand, it gathers 1 soul. You can check how many souls are in the Soul Chalice by hovering over it in your inventory. The maximum is 20 souls, when the Soul Chalice is full.
You can drink from a full Soul Chalice to gain a few powerful effects. This empties the Soul Chalice, so you'll need to collect another 20 souls to use it again.
Health Boost IV (60 seconds) (increases your maximum health)
Strength I (60 seconds)
Haste II (60 seconds)
Regeneration III (10 seconds)
Killing a Wraith will immediately fill up a soul chalice with 20 souls.
A Soul Chalice has a 35 second cooldown, so unfortunately you can't drink multiple Soul Chalices in quick succession. A Soul Chalice on cooldown can still fill up with souls, it just isn't drinkable.
Entities that are not strictly "mobs" will not fill up a Soul Chalice (boats, armor stands, etc)
Being a gold item, Piglins will steal Gold Coins, and they can be turned into Gold Nuggets using a Furnace or Blast Furnace.