The hunger mechanic is optional when creating the world, but enabled by default. It is not invasive on players who just like the exploration part and not the survival.
The hunger bar gradually decreases when the character moves, fights, or does any work.
When the hunger bar reaches 5%, the player will get "Hungry" debuff, the character will no longer have health regeneration bonuses.
When the hunger bar reaches 0% the player will get "Starving" debuff, the character will move significantly slower.
The character won't die from being Hungry or Starving, but the lack of health regeneration and movement debuff can be fatal when you are fighting monsters or raiders. So don't forget to cook and bring food with you when you go on adventures or exploration.