To add a quest, create a new page (name it Quest:Quest Name) and copy-paste the contents of the Template:Questbox onto it. Fill in the information as described on the template page, and save the page. (it is recommended to turn off the "Enable Rich Text Editing" in your Special:Preferences, it tends to mess things up)
You can also add more information and walkthroughs. Copy paste the following onto the page under the questbox, to match the rest of the quests on the wiki (remove sections that you don't want to add):
:''Type quest text here (optional) == Objectives == Type the quest objectives and tasks as described in the quest log. == Completion == :''Type quest text that you see when you turn in the quest (optional). == Rewards == * A more detailed list of rewards == Notes == Any additional details, maps and walkthroughs.