The two main types of rest are short and long.
At least an hour.
Eating, drinking, tending to wounds are typical activities.
Can spend Hit Dice at the end of their short rest, to heal.
At least eight hours.
Character sleeps for at least six of those hours.
If the rest is interrupted, the timer resets.
All HP recovered at the end.
Up to half the character's total hit dice are recovered.