To turn in a quest, you’ll first need to locate the item that the quest giver has asked you to return with.
For example: If you’re asked to return with a Bent Copper Lockpick, then go make or buy one, and return with the Bent Copper Lockpick in your inventory.
When you enter the building with the NPC who gave you the quest – the reward will automatically be given to you, and the item will be removed from your inventory.
All quests give XP as reward. Some quests give money.