For GNOME, go into Settings -> Network. Click on the gear on your Wired link. Click on IPv4 tab and set it from Automatic to Manual. Enter your IP address, Netmask and Gateway. DNS and Gateways are normally automatically filled out by DHCP.
In case it doesn't populate DNS settings, or you want to use something different, you can enter either Google's Public IPs, Cloudflares or any other free public DNS server.
For routes, the address and netmask are both 0.0.0.0 and the Gateway is usually the same as your internal IP scheme (like 192.168.0.1) The last number should be set to 1 which is the usual default for routers. Very rarely do they default to something else.
If it fails, set it back to Automatic and let me know and I'll help you out the best I can.