What role does the 'ssh-add' command play in relation to ssh-agent.exe and Error 1058?

'ssh-add' is used to add your private SSH keys to the ssh-agent. If you haven't added your key using 'ssh-add' before running an SSH command, ssh-agent won't be able to use it, and you might encounter this error. Make sure you've executed 'ssh-add' before attempting to connect via SSH.