New place, how to set up?

Hello,

Recently moved into a new place and want to get my Pi-Hole set up.

Current setup

Fiber > ISP Router/Modem > LAN > ISP Router/Modem (On 3rd floor, since WiFi doesn't reach up here)

Where should I be plugging in the Pi/Pi-Hole to have it block ads and such?

Thank you for your time.

Pi-Hole joins the network just like an other client, so wherever you can connect it so it is on the same IP range and subnet as the rest of the network, you're set.