How do I configure my router, gateway in Bridge mode?

My router (firewall actually) is connected to the gateway and both sides see the physical connection (ethernet LED lit).

Does the router need to "log in" as me to get a DHCP address?  I tried setting the router interface as a DHCP client but it fails to get an address.

My current internet, which I am switching away from once I get Xfinity working, uses PPPoE, but I understand Xfinity doe not use that, correct?

I used to be an IT consultant, used to know how to do this stuff but am very rusty!  Thanks for any advice.