Being behind a router should not mess up anything - as that's a common way of setting it up. If you can connect to the GateWayNotes (box on the wired internet connection) with your laptop, that other meshbox should connect to it as well, mesh up, and begin passing traffic.
The essential 3 steps for meshing:[]
1. Get the first box plugged into an internet (wired) connection and make sure you can surf to the internet wirelessly on it. We'll call this the "gateway".
2. Bring the second meshbox (we'll call this a "repeater") up ON THE SAME CHANNEL and with the SAME ESSID as the gateway box!! Note the
emphasis - I've seen this mistake before. I would recommend placing the second box in the exact same location that your laptop connected up to the gateway box - because we know we'll have good RF there.
3. Let the repeater box sit there for 3 to 5 minutes. Everything else happens automatically.