The cable connecting your modem and your router is an Ethernet cable, but don’t use that one, as it is important where it is.
If you just have a modem, simply make sure that it’s attached to the Cable or Ethernet port in your wall.
On your router, Ethernet ports will typically say “LAN” (Local Area Network) above them. If you’re just connecting to a modem, the port you need will usually say “Internet” or “WAN” above it.
If your Ethernet isn’t working, try using a different port on the router or a different Ethernet cable.
