Rest is defined as any activity no more strenuous as walking.

A character with the Healing non-weapon proficiency can treat six characters per day, providing an additional CON check to recover a lost hit point.

A character with the Herbalism non-weapon proficiency (which can be the same character as has Healing) can add an additional CON healing check to patients treated by the healer.

When hit points are recovered (naturally or from magic), they should be distributed randomly to existing wounds.

Characters also heal one point of Ability Score damage per day of rest, in addition to any wounds healed.  If more than one Ability Score has damage in need of healing, the Ability Score healed should be rolled randomly.