Everyone has an internal essence pool, that replenishes at a rate set by the mana level.  Unless you are special (an Adept or a Born Mage), you can only use this essence for implanting or powering Cyberware or Artifacts which work through Blood Magic: you don't have the training to move your Essence around voluntarily, so have to do it by moving your blood, which symbolically contains your Essence.

Mundanes have a Personal Essence pool of 3 x Essence + Willpower and no Peripheral pool.  Their Essence is locked at 1.

Born Mages have a mundane Personal Essence pool, and a Peripheral Essence pool of 20 larger than it would otherwise be.  Their Essence is locked at 2.

Adepts have Personal pools of 3 x Essence + Willpower and Peripheral pools of 7 x Essence + Willpower + Sum of Virtues.  Their Essence starts at 2 and can be increased in play.

Adepts who are also Born Mages have the personal pool of an Adept, but the extra 20 motes of Peripheral from being a born mage.

That gives the average mundane a pool of 6, though strong-willed people can get as high as 13.  Born Mages start around 9+20, and could in theory go as high as 16+20=36.  Apprentice Adepts start at 12+29, full Adepts are about 20/48, and in theory an Adept could get up to 28+72=100.

See HouseRulesOnTaint for the effects of using your Peripheral pool.

The Cyberware background changes your Essence pool.  See HouseRulesOnCyberware for details.

Normal people recover Essence at a rate of 4 motes per hour of sleep.  Those trained in Essence use (e.g., Born Mages, Adepts) can meditate to recover Essence at a rate of 2 motes per hour.  Being in a level N Demesne to which you are attuned increases your recovery rate by 4N.  Bearing a Hearthstone from a level N Manse to which you are attuned increases your recovery rate by 2N.  You can only benefit from one Demesne or Manse at a time.  Having the backgrounds Cult or Karma Ritual can increase your Essence recovery as well --- see HouseRulesOnBackgrounds.

<hr>
This is an official mechanic; please leave hacking on ExaltedHackingEssencePools.  Comments are still welcome here.