Use the Rest button during a session (out of combat). A short rest (~1 hour) lets your character spend hit dice to heal — roll them physically, submit the total — and recharges short-rest abilities.
A long rest (~8 hours) restores the whole party: full HP, all spell slots, class resources, half your hit dice back, and one level of exhaustion removed. The DM narrates the camp, the watches, the passage of time.