Talent trees on the different characters is where you choose what kind of spec you want to have on your character. Example: If you want to be an Holy Priest and do healing or Shadow Priest and do damage. Most of the talents are passive, and give you different boosts. But some talents are also Active, and then you would need to Bind the talents. Have a look at the Basic Configuration section on how to bind the talents with the Talent ID.
What the talent does, says in the talent description! And you earn talent points at different levels. 3-4 tiers on the talent tree. You would need to spend x amount of talent points in Tier 1, to be able to spend talent points in Tier 2 etc.