On this page of the Assassin's Creed Valhalla Wrath of the Druids game guide you will find a detailed walkthrough of the Giving Your Words quest.
By rebuilding the trade post in Lisdurrow, you will have access to Books - one of the main luxury goods in the Wrath of the Druids expansion pack.
Reward for completing the mission: 1,700 XP.
Investigate the Trade Post
Once you have cleared the trade post, read the note attached to the bag in one of the side rooms in the location marked in the image above. You will learn where to look for the document you'll need to rebuild this trade post.
Obtain the deed
Head to the location indicated on the world map and use Odin's Sight to locate the chest containing the document. The easiest way to get inside is by using the explosive arrow - just blow up the rubble and then shoot off the door lock.
You will find the deed to the property in the box marked in the image above. Take the document and return to the trading post in Lisdurrow.
Restore the Trade Post
Return to the trade post in Lisdurrow, interact with the wooden plaque and confirm the construction of the new building. This will complete the Giving Your Words quest and you will receive 1,700 XP as a reward.