not sure why HDMI isn’t working for you, you might check the config file
SSH is meant to login from another computer. My Sprinkler Pi is in the basement, and I don’t want to drag a screen and keyboard down there. Since it’s on the network, I can login from any other computer using an SSH client (terminal on a mac, putty on windows, if you’re using Linux you don’t need help). I can edit the python files and do whatever other configuration I need, but from the comfort of my couch / laptop.