OK, you’ve got your google fiber box, and now a second “better” wireless router (we’ll call it router 2) that you want to basically use instead of the built-in wireless of the google fiber box? This is the place for you. (reasons for doing so: some routers seem more consistent/have better range than the google fiber box, or more advanced networking protocol, like 802.11ac [gfiber box has 802.11n, slightly older than 802.11ac FWIW]).
Basically, by default, router 2 will want to “live” at 192.168.1.1 [the same place your gfiber box does]. So…turn it on, not connected to your gfiber box yet, connect to it [wireless or wired], navigate to 192.168.1.1, then change it so that it’s “LAN IP” (or whatever your equivalent is) is, say, 192.168.1.200. The reason to do this is so that it will leave at a different space in your network than the gfiber box, so that if you need to go to its admin [in the future] you can browse to 192.168.1.200 [if you left it as its default, it would basically "conflict" with the gfiber box, so if you navigated to 192.168.1.1 sometimes you would get the gfiber box, sometimes router 2--weird--we don't want that].
Also look around for something that says “dhcp” and disable it [since you'll already be getting dhcp from the gfiber box, you don't want/need it coming from both in competition].
Save configuration on router 2.
At this point, you could optionally go to your gfiber “advanced” panel -> services -> IP Address Distribution -> Dynamic IP Range click “edit” icon, make the max it will assign as 192.168.1.199 [so that it will never accidentally conflict with the hard coded one we assigned router 2]. You may never get as high as 200, however, so might never need this.
Now, connect an ethernet cable from one of the LAN ports on the gfiber box, to a *LAN* port on router 2 [not a *WAN* port].
At this point, you should be able to connect via WiFi to router 2 and it should give you internet access [woot]. The reason this works is that, basically, when a client connects, it will send out a dhcp request (“give me an ip address! and tell me how to route packets to a gateway to the internet!”) to which the gfiber box will respond “pick me! and route through me” so basically it has turned router 2 into a “dumb” terminal, just forwarding packets between the gfiber box and your new router.
(As a side note, if you go to the admin interface of router 2, at this point it will show you failure warnings like “unable to connect to WAN!” which is actually expected–it isn’t connected to WAN, it’s basically just port-forwarding for you on the LAN, so disregard).
Now you can go back to your gfiber config and disable its wireless [if you want it that way--you probably do, since why have two routers competing in the wireless space? but you could leave it on].
Also possible, but out of scope here: you could make router 2 be a “repeater” (same bandwidth, same SSID) as your gfiber box. So put it somewhere else in your house, theoretically, it extends your coverage overall.
Also possible, but out of scope here: you could make router 2 use an “opendns” configuration–which basically adds a “safety feature” to your global internet.
Worked for my