The primary cycle of your economy is formed with 2 elements: an underwater volcano, which produces bubbles when touched and your submarine base: it converts oxygen into money.

The first purchase is the hammer. It hits the volcano automatically. Then you'll be able to connect a cogwheel to it. By spinning the cog you'll be able to empower the hammer in a great way and increase your earnings.

There is much more to discover, the ingame tutorial will explai you the rest!