To setup parameters for a user to enter, go to the Field Explorer screen, right click on parameter fields and select new. The screen will ask for a name, a prompt and a type. When you run your report, the prompt will appear and give the user a field to enter the data.
For you, you could call it lowrange. The prompt would be 'Enter the low number of the packing slip range' and give it the appropriate type. Use the name of the field (lowrange) in your select statement or as a variable in your report.
Do the same for highrange.
Good luck !