Concepts to consider

looking at the ssh manual

 ssh destination [command [argument ...]]

This means that you can use commands while we access

bandit 18

Task

The password for the next level is in a readme file on the desktop, but since we cannot access bandit18 we will have to execute the command while entering

Solution

Then we use:

ssh bandit18@bandit.labs.overthewire.org -p 2220 cat readme

bandit18@bandit.labs.overthewire.org's password:
awhqfNnAbc1naukrpqDYcF95h7HoMTrC