From what I've read (grossly oversimplifying) in a feudal system king owned all the land and would give parts of said land to his knights in exchange for military service.
The knights would, in turn, divide the land into smaller chunks and let peasants use these chunks in exchange for a part of their produce and/or money.
Where did the king's goods/money come from then?
The possibilities I can think of are:
- he lent only a part of the land in exchange for military service, while the rest was providing income instead
- king's income came from taxing the trade
- in times of peace the knights would pay rent, while at war their military service would replace the rent
However I was not able to find any confirmation for these.