Your post provides no indication as to which fittings might be missing, so no one can tell you. It’s like saying “My car won’t start.” Perhaps it’s out of gas. Perhaps the distributor is disconnected. Perhaps you have to depress the clutch. Perhaps the battery is dead. There are too many variables involved. Pictures of the boat and rig might be helpful. In the meantime, the best advice might be for you to look up Designers Choice 15 Sailboat on Google, under images, and look to see how the boats are rigged. That may show you what you’re missing and what you need to do. A rigger might also be able to help you, though that might be more expensive than a Google search.