These systems are components of the Hardcore Ruleset (HCR).
When you successfully attempt to rest, a conversation will appear which will offer the available choices.
Limited Rests Per Day
Resting is limited to once very eight game hours (16 real minutes).
PCs must also have a food item, or they will not be allowed to rest. One food item is consumed with each rest.
Resting does not fully heal characters. Instead, either one or two HP per level is restored when a PC rests. Because of functional limitations, this is accomplished by magically damaging the PC from full HP after resting so the correct HP total is reached.
Characters heal 1 hp per level on rest without a bedroll, or 2 hp per rest with a bedroll. Barbarians, druids, and rangers heal 2 hp per rest with or without a bedroll because of their expertise in survival.
Public inns, PC residences, and guild buildings offer increased healing when resting.
Note: This is because simply resting should not fully heal a wounded PC of all injuries, and in PnP it does not. The natural healing of wounds takes time.
Resting in Heavy Armor
Resting in heavy armor (base AC6 or better) will fatigue your character, resulting in slowed movement with penalties of -2 to STR and -2 to DEX.
Resting in heavy armor while fatigued will produce exhaustion, resulting in slowed movement with penalties of -6 to STR and -6 to DEX.
The rest conversation will warn you and give the option to remove heavy armors.