My 2001 dodge durango will run, but once i park it it wont start again. If i play around with the shifter the truck will start, What is wrong with it?

Is this an Automatic transmission? If it is, and what is happening is that when you turn the key the starter will not engage, then you play with the shifter nob, and then it will start, then it is the
NUETRAL SAFETY SWITCH.

This is there to ensure that you cannot start the car in a gear, and will only start in either Park, or Nuetral. They go bad, just like anything else. Try starting the car with the gear-shifter in the NUETRAL position. I bet it will start.

Where the switch is located on this car, I am not sure, but it is not an expensive fix.