A quest tracker answers "what do I do next" without needing to open a menu. A title (the quest name) sits above a list of sub-objectives; completed ones get a checkmark plus a strikethrough or dimming, so open and done are distinguishable at a glance.
The moment an objective completes deserves its own animation — a check pop, a bit of progress bar filling in. It's the inverse of the Zeigarnik effect (unfinished tasks nag at attention): a clear completion signal is what lets the player mentally close the loop. With several quests active at once, surfacing only the nearest one (or the one the player pinned) up top keeps the tracker from sprawling into a wall of text.
Cram too many quests into one tracker and information overload means none of it gets read. Limiting active quests to a small number, and pushing the rest to a separate quest log screen, is the standard approach.
When to use
In-play screens for open-world or RPG games juggling multiple objectives. Overkill for linear stages with a single goal.