While exploring the mines, you find different resources and expendables that would help you in your playthrough. Those are:
Gold - your main currency. Use it to hire new goblins and upgrade buildings. You earn some amount from destroying stones: a higher stone level means more gold. Forge and Shafts are stable sources of gold for your needs. You can also get huge amounts of gold from mystical barrels.
Elixirs - a magical substance required for your magical researches. When you use cards to increase a jewel level or improve other processes in your mines, you have to spend some elixir to proceed with the research.
You find elixirs almost everywhere in the game: inside the stones (even regular ones), in chests obtained from checkpoints and shafts, and get them as a bonus when upgrading your shafts. If you're eager to finish some important research ASAP, you can buy the elixir pack from the game's store.
Gems - an extremely rare special currency used to buy items from the store. It can be obtained from specific stones on the map, high-level chests, and from Spinning wheel. You can also get gems as a reward in special events or buy them in the game store.
Time potions - magical items that let you travel in time! The time skips forward, all timers are reduced, and you get the gold that would've been generated in a corresponding timeframe.
There are only two ways to get a potion: buy one in the game store, or win in the spinning wheel. Keep in mind that the small potion activates Immediately! Make sure that everyone is ready for the time skip.
Cards - unique items used in magical research. Cards are required to upgrade jewels and get your shafts automated. You can also unlock multiple other bonuses! Like improving your forge, goblin cannon, or all shafts at once! You can only drag cards from chests or earn as a reward in special events.
Chests - useful boxes with lots of precious loot! Usually contain cards and elixirs, but might also contain gems. Weekend events chests might also contain crowns.