To connect to your nas via ssh you dont have to use the Webinterface
you have to use a ssh programm.
If you are new to Linux pleas be very careful if you login as root. because as root you can do everything on your NAS including deleting all your files and the OS files too so that your system doesnt work at all.
users install ssh or open-ssh via packet manager and insert in a console
where xxx.xxx.x.x is the ip of your NAS
then it starts interacively to ask you if you acept the key and asks for the password
(if you tip a pw in *nix you dont see any feedback during tipping nor the letters you tipp nor stars)
the $ is not to insert it just shows the reader that it is an input same as the # which shows you that it is an input with root rigths.
users can use the programm putty to acess via ssh.
I don't know it by hart but it should not be so hard to acess your NAS with it. The concept is similar acesscing via a Linux terminal.