Ad farm like many other games The game is very simple - just match soldiers with greater number. It’s all made to farm those ad money - on every action you can watch a video to give the creator revenue and help him make more uninteresting games.
There is also a bug - if you spam the “gold” option, you can get infinite money, after which the game will bug out to a negative integer and you won’t be able to buy anything else with negative gold (not that you have anything else to buy, because you’ve maxed your stats)