The Crusader is an NPC in The Town that allows you to access your daily quests.
Stand near The Crusader to bring up the daily quests window.
You will gain a new quest every day for each of your characters.
Complete a quest by clearing the dungeon indicated by your quest (on the indicated difficulty) and then returning to The Crusader.
If you successfully completed the dungeon indicated on the indicated difficulty, then the quest should be colored green. Click on the green quest to complete it and receive your reward.
Upon completing one of your daily quests you will receive one or more of the following rewards:
1. Experience points
3. Immortal rarity items
The level of the immortal items will vary depending on the level indicated by the quest that you completed.
Note that you will not receive immortal items that are unique to a specific dungeon.