Healing

Hit Points can be restored by magic, such as the Cure Wounds spell or a Potion of Healing, or by a Short Rest or Long Rest.
When you receive healing, add the restored Hit Points to your current Hit Points. Your Hit Points can't exceed your Hit Point maximum, so any Hit Points regained in excess of the maximum are lost. For example, if you receive 8 Hit Points of healing and have 14 Hit Points and a Hit Point maximum of 20, you regain 6 Hit Points, not 8.

Resting
Adventurers can't spend every hour adventuring. They need rest. Any creature can take hour-long Short Rests in the midst of a day and an 8-hour Long Rest to end it. Regaining Hit Points is one of the main benefits of a rest. The rules glossary provides the rules for Short and Long Rests.