I just paid attention to what you asked....lol.
The practical is basically a really detailed flight plan. For us, the examiner uses a 727. You're given the weather for the departure, destination and all of the enroute weather. You also get the flight info, which tells you the number of PAX, the amount of cargo, any MEL'd items, NOTAMS, etc, etc.
From that, you have to do your thing, determine if an alternate is required (pretty complex process in the 121 world), what alternates are legal, fuel required, takeoff and landing weights, etc, etc.
If you can do it and come up with numbers that match his (+/- a reasonable margin for human error), you're a dispatcher!!