Lets you auto skip gossip, complete quests or accept quests. You can add quests to be accepted/gossip skiped by holding the ALT key down and clicking the quest you want, and if you hold down CTRL and click the text it'll auto accept the quest. Quests that have item requirements have to be completed manually once so it can learn the item requirements.
It can automatically figure out what quests to auto complete so it'll always use the highest turnin one when available, for example if you have 23 Sunfury Signets it'll do "More Sunfury Signet" twice, and then complete Single Sunfury Signet three times.
Auto skipping/accepting can be disabled by holding down SHIFT before talking to the NPC, and you can remove things by holding down ALT + Clicking again, or CTRL + Clicking