You enable SSH (most use
LAN Only) in the router's GUI interface (Administration > System > Service). The default port (which can be changed) is
22. Then one uses a SSH client program (For example on Windows,
Putty is popular) to SSH into the router and issue the commands to list, save or modify the NVRAM values/parameters.
Standard warning on editing or modifying NVRAM values. Incorrectly modifying the NVRAM values can lead to unexpected router behavior, even out right bricking of the router. Proceed at your own risk!