First you need a tend account, this is very easy, only go to https://tend.io and start the trial following the site instructions.
When you have your account, copy the Script in the Tend Dashboard
Now access to your Ordering Builder and set the script in the Third-party section
And Start to work!
When a customer completes an Order, you can track the customer in the Tend Dashboard.
Have a nice ordering
Regards, Marcos Beltran