The Google WiFi primary unit (the one connected via Ethernet to your internet service) is a router and a firewall that creates a new "inner" network that is separate from the "outer" network it's connected to. It sounds like you have wired devices connected to that "outer" network already. If you only have one single Google WiFi unit, you can put it in "bridge" mode, but that will mean losing the ability to add multiple mesh/secondary units, guest WiFi, and some other features. The recommended configuration is to have the primary Google WiFi unit be your router+firewall for WiFi and wired devices connected through its "LAN" Ethernet port, which is part of the "inner" network it creates. If you have multiple wired devices and/or an existing house-wide Ethernet network, you can pick up an inexpensive unmanaged Ethernet switch to expand that LAN Ethernet port to make more available.