// load the preference object
zkups__UPSShipmatePreference__c pref = [SELECT Id,Name from zkups__UPSShipmatePreference__c WHERE ID = 'YOUR_PREFRENCE_ID'];

// Create the new shipment object
zkups__UPSShipment__c  shipment = new zkups__UPSShipment__c();

// set the tracking number of the shipment you'd like to add
shipment.zkups__MasterTrackingId__c = '1z1w7w420374732280';  // live example

// Set the preference ID
shipment.zkups__UPSShipmatePreference__c  = pref.Id; 

// Set the ModKey (enables you to edit the shipment object)
shipment.zkups__ModKey__c  = 'Please email support@zenkraft.com to obtain';

// Insert the shipment object
insert shipment;