Mine deeper underground to obtain more resources and minerals to sell. You'll also encounter treasure chests the further you dig. These chests contain random rewards from small to huge sums of money and resources.
While mining, you'll eventually reach the underground city. At this point, you'll be introduced to new resources and a pyramid where you'll find quests to complete.
𝗨𝗽𝗴𝗿𝗮𝗱𝗲 𝘆𝗼𝘂𝗿 𝗴𝗲𝗮𝗿
You start the game with a humble shovel for digging. When you earn enough currency, you can upgrade your digging methods, from shovel to jackhammer; drill to nuclear excavator when you earn enough currency. Beyond that point, upgrades get supernatural, with workers being replaced with aliens and demons!