Yamaha AG03, Cubase AI, Yamaha usb piano, w10 pc

This is an appeal for help. For someone with a similar setup to talk me through the basics.

I use a windows 10 pc, of sufficent capability.

The AG03 interface came with the Cubase AI version, and the Steinberg ASIO, which all seeem to have loaded okay. The piano is the Yamaha P45 with usb connection. The piano worked with Ignite but the latency was dreadful. So upgraded to the AG03.

I have my guitar, vocals and piano headphone output all go into the ag03. It is connected by usb to the pc. then the ouput to the speakers from the ag03.
So fairly confident all that is working. But it might just all be doing it in analog (simply passing through the AG03) and ignoring the usb stuff. I cant tell.

I have seen some indication via sound level displays that the piano is detected. But so far can not find how to record.
There must be untold things I need to set, and I was just assuming it woud all be done automatically, but that isnt how it works.
I need a start point to get something working. That should help get my bearings and can then i can improve on that.

So if anyone could take me through to the record stage, Id be grateful.