The Instant APs are Access Points, not a router (in basis). Consumer router/APs combine a router function (WAN/LAN) and the AP (provide wireless connectivity to the LAN segment of your router).
Instant APs are designed to connect to an existing LAN network like you have in most businesses. That is why you don't have a WAN interface to be configured. There are some exceptions where you can use the Instant AP as a router, but in most cases, you deploy it like that only in branch networks and as part of a larger solution.
If you have a router with multiple LAN ports, just connect the Instant APs to those LAN ports.
Official Aruba Instant training videos (that do expect some basic networking knowledge): https://www.arubanetworks.com/products/networking/aruba-instant/instant-training/
And I recorded some short demo videos on how to get started (also with some expected basic networking knowledge) on the Airheads Broadcasting Channel on Youtube.