Hi there, Alex from the art team here.
First off, thanks for the support on being interested for this game. (this means my art is nice heheh) And yes, the game can be confusing even for me when I played for the first time and the description is kinda unclear on the actions too. So, I'll be adding instructions on how to play based on my experience.
1) During day phase, you can only build buildings and buy items from the shop.
2) Buying buildings = more human population = more money generation.
3) End turn multiple times to allow the buildings to finish building and end day phase
4) During night phase, click on the warriors to deploy. Changing places is allowed at this time.
5) After starting the fighting phase, you can choose to move and attack once for each warrior. There is no order on which should be done first.
6) Selecting a warrior will show the places that he can move to. Be careful that you can't change places after placing them to a spot during that turn.
7) Select a weapon and select an enemy to deal damage to it. Some weapons deal more damage and have a wider range
8) Protect the houses! The game ends if you lose all of them. But the warriors will respawn with one health after going through a day phase.
9) The cycle continues...
Hope you enjoy the game after understanding the basics of this game! Pro tip: attack before moving allows dodging ;)
Addition answer to your question, the population showing zero is a bug, but it doesn't affect the gold from generating.