You can setup your job(s) to use the new online ordering experience a few different ways:
During new job setup
Inside the job settings of an existing job
Using the Quick Edit tool from the Jobs tab
When creating a new job, you'll see the New Shopping Cart (BETA) section on the first page of the New Job Setup wizard:
For existing jobs, you'll find the setting under Job Settings > General > New Shopping Cart
You can also select multiple jobs at once and use the Quick Edit tool to make the switch: