Most everything you do costs turns. Once you run out of turns there is nothing you can do but wait for more. Turns are regenerated 3 a minute and you can save up to a maximum of 6000.
How much turns are used for certain actions?
Cooking - 5 turns
Farming - 1 turn per picked up item
Fighting - 10 turns
Fishing - 1 turn
Picking up items - 1 turn per picked up item, with a max of 10
Walking - 1 turn
Chopping Wood - 5 turns