Others have touched on this but I’ll go into some detail how it works for Holy Paladins.
Some abilities, Holy Shock the important one for Holy Paladins but we also have a talent that will give you a point for directly healing your Beacon target ,will generate one point of Holy Power up to a maximum of three. These seem to degrade over time but I’m not sure at what rate. Holy Power is then released by casting our new mana free instant heal:
Word of Glory
40 yd range
Instant
Consumes all Holy Power to heal a friendly target for 1553 to 1729 per charge of Holy Power.
The UI now was a Holy Power resource thing under your characters portrait.