Speak to Captain Arellius, who is in the Ruins on the dock. ( -160, 0, 80 ) /waypoint -160, 0, 80. This closes the quest, and starts you on the Ruins quest series.
Note: If you are not yet level 10, then you should work on the other quest series within the Freeport Districts Timeline first, before proceeding with the Ruins quest series. Follow the dialogue with Enforcer Kurdek to get directions to the start of these quest series.