First task is easy. Simply look left to see a table, then place all four compass pieces on said surface to make the device. Lovely. Next, hop off and grab a Skif. The entrance to the Lighthouse is in the North West. You know the drill by now. The switch to open the gate is up on the ledge to the east of the gate. Not far, just use the ladder.
Once in the lighthouse zone, head forward into the small shanty. Deal with the pirates and then take the path to the right, up and around towards the lift on the platforms.
There are a lot of pirates around here, deal with them as you see fit.
Ride the elevator up and you'll come to a large grassy area. There aren't any enemies here, yet, but there will be later. Use that knowledge as you want. Anyway, head into the lighthouse and ride up to the top, placing the compass pieces into the top of the lighthouse to finish this mission.