This is where it basically starts, and its really short. Go to Fort Hraggstad , (which is west of Solitude ) and when you arrive, you’ll be greeted by three or four bandits, as well as four archers on the outside of the Fort. Take care of them all, loot the place and go inside.
If you had the quest "Join the Stormcloaks" it will now have FAILED, since you can only pick one side or the other.
You’ll have two bandits on this first floor and upstairs, you’ll find the Bandit Chief looking at something on the table. Sneak attack him and look at the table for an Archery Skillbook "The Gold Ribbon of Merit".
Now leave and enter the Hraggstad Prison on the east side. Kill the three bandits in here and grab the chest near the cells and the quest is now complete. Fast travel back to Solitude and speak to Legate Rikke . She’ll tell you that to officially join the Legion, you need to speak to Tullius to swear the Oath. Speak to him and repeat the Oath. This ends this quest and starts the next one.