Can anybody link me or juts explain how to heal with holy light, and what build should i use? do i need to wait for the tank or any other player to get to like 50% hp or just spam it like i would spam FoL, thank you
The choice of spamming Holy Light is very dependent on the situation. As Holy Light has a longer cast time than Flash of Light, you can expect more damage to reach your target while you are casting, which you have to take into account. Imagine Festergut having inhaled three times, thus dealing much more damage to the tank, this will be more of a spamming situation than healing in the early stages of a Deathbringer Saurfang fight.
Blindly spamming Holy Light will sooner or later (depending on your mana pool, the fight's length, etc.) drain all your mana, so take the fight's mechanics into account.
First and foremost you should cast the right heal for the right time. PLEASE don't think a "Holy Light Pally" will constantly spam HL exclusivley.
When to use HL depends on the fight, the tank, and your gear. You should use FoL until you start to fall behind, then HL to top off. IE FoL until the Tank is about 1 Holy Light from being topped off. In 5 mans you won't be using HL most of the time, but in raids the damage is much higher, and you will use HL much more, almost exclusively on some fights.
The two build linked by ImpartialSanity are the basic Holy builds. A point can be taken from Imp BoW and moved elsewhere depending on group comp. And as said, your primary goal is to be a mana monster, stack int almost exclusivity, several enchants are better and you need to activate you meta.