A yellow exclamation mark over a character's head means they have a quest for you. A yellow question mark means you can hand one in. Press L to open your quest log, where you can track, share or abandon quests. The quest log key and abandoning when the log is full are from Blizzard's starter guide.

Reading the marks

Mark Meaning
Yellow exclamation mark A quest you can take
Gray exclamation mark A quest you can't take yet, usually because your level is too low
Yellow question mark A quest ready to hand in
Gray question mark A quest you've taken but haven't finished

Tracking

Tick a quest in the log to show its objectives on screen. With the Enhanced preset, the map also shades the area where the objectives are. See Classic or Enhanced.

Quest level colors

The quest's name in the log is colored by difficulty: gray is trivial, green is easy, yellow is right for you, orange is hard and red is very hard. Gray quests give little experience, so drop them if your log is full.

Sharing with your group

Open the log, select the quest and click Share Quest. Groupmates who can take it get a pop-up. It saves everyone running back to the quest giver. See inviting someone to your group.

Abandoning

Select the quest and click Abandon. Its quest items disappear. You can usually pick the quest up again from the same character.

Stuck on a quest

For where to quest next, see the leveling route.