First, make sure your gas cap is tight. It might take 20 mins of driving after tightening for the light to go out. Check the gasket on it too to make sure it doesn't leak air. Replace if there is any doubt.
A service engine light means you have a problem that needs repairing. If you have already checked out the problems and corrected them, disconnect the negative cable from your battery for 1 minute. If the light comes back on after reconnecting the battery, you still have an unresolved engine problem.
additional info : there is no "reset button". The trucks Computer Monitors various systems and if it senses a problem it turns on the light. The computer also stores codes that can be read and interpreted giving you a hint as to what the problem is. When the problem is fixed the computer should show no issues and the light will not light up. If you have a truck with a digital tripmeter/odometer on the dash you can access all the engine codes by pushing the reset button while you start the engine. After the engine starts continue pushing the reset button to display things such as a digital tachometer, water temp etc etc. This is there because the computer is generic to all trucks but not all trucks have the fancy option package of showing this info on a separate screen. What you are seeing is what the dealer would see with his diagnostic computer. It is all alpha numeric and makes no sense but you can find explanations to all this on several websites dealing specifically with Ford trucks. Its out there on the web, you just have to dig. Good luck.