Channel Energy

Channel energy is a power granted to Clerics (as well as Paladins and some others), through which they channel their divinity to damage foes or heal allies around them.
Good aligned clerics with this ability channel positive energy, which can damage undead creatures or bolster the living.
Evil aligned clerics with this ability channel negative energy which can bolster undead creatures, or damage living creatures.
Neutral aligned clerics must choose when this ability is first unlocked whether to use turn undead as a Good or Evil aligned cleric, and cannot reverse their decision once made.

Channelling Energy

Using channel energy is a standard action, and can only affect one type of creature (undead or living) each time it is activated. This ability is a 60 ft burst, only affecting targets with line of effect to the caster (not in total cover). A cleric must present their holy symbol to use this ability.

Healing

Good aligned clerics targeting living creatures or Evil aligned clerics targeting undead creatures heal all affected targets in the burst for 1d6 points, plus 1d6 points for every two cleric levels they possess.
Bolster Undead: Rather than healing undead, clerics channeling negative energy can instead bolster them against future turn attempts from good aligned clerics. Bolstered undead add the bolstering cleric's Charisma modifier plus half their cleric level to the next Will save made against a channel attempt, take only half damage if they fail that save, and take no damage on a success. This effect lasts for 10 minutes.

Damage

Good aligned clerics targeting undead creatures or Evil aligned clerics targeting living creatures damage all eligible targets in the burst for 1d6 points of damage, plus 1d6 points for every two cleric levels they possess past 1st (2d6 at 3rd, 3d6 at 5th, 4d6 at 7th, etc). Affected creatures may make a Will save (DC = 10 + 1/2 the cleric's level + the cleric's Charisma modifier) to take half damage.