what is " fields: 'id' " in the below code? :     /*In the below code I am trying to create folder*/
    
    var fileMetadata = {
      'name' : 'Project plan',
      'mimeType' : 'application/vnd.google-apps.drive-sdk'
    };
// what is fields and resource key being used
    drive.files.create({
       resource: fileMetadata,
       fields: 'id' 
    }, function(err, file) {
      if(err) {
        // Handle error
        console.log(err);
      } else {
        console.log('File Id: ', file.id);
      }
    });
  // what this fields: id represents.
