Follows are command lines that I often use (not necessarily the best approach) while interacting with ip, which is used to show / manipulate routing, devices, policy routing and tunnels.
Show current routes.
ip route show Add route:
sudo ip route add `a.b.c.d/e` via `gateway_IP` dev `device_name` a.b.c.d/e can be the subnet of IPs or just an IP address of the desired destination, and the gateway_IP is the IP address of the gateway where you want to route your traffic through (e.