Using Google App Script to find rental cars

Sorry for the rather generic title but making no assumptions on technical solutions…

I am new to Google Apps Script but learning fast. As a fun personal project, I want to build a small application which goes off to Avis and retrieves rental car prices and availability.

I have registered with developer.avis.com and successfully run the following code snippet:

function avis(){

  var avURL = 'https://developer.avis.com/swagger/spec/car_availability.json';
  var avHtml = UrlFetchApp.fetch(avURL).getContentText();
  var avDoc = JSON.parse(avHtml);

}

avDoc comes back as nice structured JSON with all the parameter fields the Avis document says will be needed to retrieve a rental quote.

I assume I now need to fill the parameters in and get avDoc back over to Avis.

But how ? Please indulge this total noob with pointers on how to do so !!

Thanks