Basic definition of a Windows Service is a program with no (or very little) user interface which provides programmatic services on the computer on which it is running. Real services though is registered in Windows' Service Control Manager Database and can be started, stopped, restarted, configured via the Services mode of the Computer Management Console.
However, if your need is just like mine, i.e., a VFP app continuously running in the background just to do some things for my other app, then this simple demo which does not really put the exe among the Windows Services is enough. What it will do is create a system tray icon to tell you it is running, then run continuously and on a specific time (which I control via passing the time as parameter to make it more flexible) will perform something for you (whatever you want that is possible).