vnc and ssh on mac

I’ve setup a vnc server on my iMac at home and a vnc viewer on my macbook.
It works fine using port 5901, both on the same network and outside. When i try to use ssh to connect I get cna’t connect needs password. 2 questions on the viewer what is my ssh username? and what is my password?. I’ve tried all the passwords i have and it does not connect.

could someone please set me straight on using ssh on my machines, go slow on a poor old man