It's a system called Yoello, I've never heard of it before but from what I can see I think you go to the restaurant, scan a QR Code with your phone (not via an app, via the website) - that then gives you access to the menu, and ability to order and pay. Whether you do that in the restaurant then walk over or do it from the table I have no idea, from the table though probably for social distancing reasons.
Walesonline have confused the issue by sharing a tweet from FORCardiff encouraging people to download the app but their tweet is aimed at getting businesses to sign up, not customers. As far as I can see it's not exactly been explained yet how it'll work for customers, maybe there'll be instruction boards put up or something. It won't be rocket science though.
I think with the seating area not being in the venue I'd imagine you have to pay upfront which rules you out unfortunately. Unless a Pizza Express or somewhere else that you know what you're getting signed up?
https://www.walesonline.co.uk/whats-...-open-18677644