Error while logging through ssh on ubuntu

Solution 1:

Looks like you missed the username. On a Raspberry Pi, the username is usually "pi" so if you want to run the ls command on the Rpi from your Ubuntu computer, the command should look like ssh pi@ipaddress ls and it should prompt you for the pi password. ssh will run the ls on Rpi, send the output back to Ubuntu, and then finish by handing control back to the Ubuntu session.

The "pi@ipaddress" section corresponds to the "destination" placeholder in the usage guidelines you mistook for an error. The complete documentation can be seen by running man ssh but that can be overwhelming to a beginner.