Sounds like you already successfully added your script to the toolbox, so you're close. You just need to set the parameters that are listed in the script within ArcMap if you want to run the script as a tool. In your catalog, right click on your script tool that you created and click on properties. You need to define your parameters under the parameters tab.
So, you would set your first parameter up like this:
Display Name - polyFC (or whatever you want it to be displayed as in the tool)
Data Type - String
Under parameter properties, you would set the following:
Type - Feature layer
Direction - Input
You can then add the rest of your parameters, though the parameter properties and types may be different depending upon how they are used in the script.
The only other thing to note is that parameters defined in ArcMap need to be in the same order as the ones defined in your script.
Here's a good page on setting parameters: http://desktop.arcgis.com/en/arcmap/10.3/analyze/creating-tools/setting-script-tool-parameters.htm
And here's the page that lists all the different types of parameters (sometimes all the different types can get confusing, so it's nice to have a list!): http://pro.arcgis.com/en/pro-app/arcpy/geoprocessing_and_python/defining-parameter-data-types-in-a-python-toolbox.htm