Stamina is replenished naturally, consuming hunger.
Not all actions consume stamina. For example we don't want to slow down exploration, so sprinting does not consume stamina, but you can only sprint if your stamina is above a certain level.
When using a tool or weapon stamina decreases depending on its weight.

This has the potential to add a lot of depth to fighting and crafting. For example a low-range dagger might mean that you get hit more often, but consumes less stamina than a long range spear.
But as you get more stamina conserving in your combat style, or against certain bosses, the spear might be the better option.