The "merge" genre is basically part of the classic Match 3 formula. But instead of trying to match three items of the same color or shape, in Merge games, you combine two similar structures with a new, larger and more valuable item. In our case, you start turning metal coins into large coins that will turn them into gold, eventually - after enough assembly - into large shiny jewels of different colors.
All items on the deck automatically earn money so the more valuable the item, the more money you will earn. And this money will allow you to buy more valuable gems instead of doing a hard work of joining them together. This means you don't have to start by combining the least precious metals and save a few steps down the road.
A new gem will appear on the deck every 10 seconds, as long as there is room for them. However, you can speed up the process by tapping the corresponding icon on the right. As you combine gems and earn more money, you will upgrade your deck and gain more space to place your gems.
Basically all you do is touch or click the screen, merge gems, earn money, tap a little more, combine bigger gems, get more coins, hit harder, merge the biggest diamonds you've seen, and earn even more sweet prizes money! It's a never ending spiral of touch and reward, and ultimately satisfying.