D20 Quests are story driven perks that you can apply to your D20 Profile. These perks are custom built around your character and the story that they went through and it reflects the power increase your character should get after a lengthy storyline.
As you level up through the D20 system you will have the opportunity to gain Quest Traits. These are custom traits that you the player create to fit your character and really make it your own.
The Quest Traits are gained through IC story progression. In order to gain your requested trait, your character must go through a 2-3 event long personal story arc that the guild participates into some degree. It could be any manner of a story arc that you wish to put your character through and you will be assisted by the officers to ensure the experience is how you want it to be.
You will work with an officer or GM to ensure your proposed trait is not only fitting for what you wish to accomplish but also is powered correctly within the system.