Periodic Quest
The Periodic Quest widget gathers the server's quests — main story and recurring ones — into one window. Quests are grouped into tabs, and each one shows its reward, its requirements and, when available, an Add Quest button to accept it and a Location button to reach it. Open it from the widget menu at the bottom right of your screen: the Periodic Quest icon
is in that list.

Main Story
The Main Story tab holds the main quest of every Act: this is where you take them, NPCs no longer hand them out. You can hold one main quest at a time — finish the one you have before accepting the next one. Full route in Leveling Character.
Requirements
A quest is available only when you meet all of its conditions: the required level, the required Hero level, and it must not already be in progress. Daily and Weekly quests are limited per account (once per day / per week) and stay locked until their reset.
Location
Quests with a location have a Location button that teleports you there after a 5-second delay. You must be in a normal map or rift, with no shop open and not in an exchange.