WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
Align the fuel tube fitting and push together until a click is heard.
Fig 1: Aligning Fuel Tube Fitting
Courtesy of FORD MOTOR CO.
Pull on the fitting to make sure it is fully engaged. Install a safety clip.