You would just need to create an entry for eth0. Using nano may be easier for you if you aren't familiar with vi.
Add lines like the following under the lo interface.
For DHCP it would look like this.
For a static ip, it would look something like this (obviously tailored to your subnet).
iface eth0 inet dhcp
To save your changes, press Ctrl+x following by Ctrl+y.
iface eth0 inet static
dns-nameservers 192.168.0.1 126.96.36.199 188.8.131.52
Then, restart networking to enable the changes.