Download and Install PuTTY from below link
open PuTTYgen and click on Generate
Enter password in Key passphrase and confirm passphrase.
Now click on save private key and save it.
login to Linux server shell and authorize public key in that
mkdir ~/.ssh chmod 0700 ~/.ssh touch ~/.ssh/authorized_keys chmod 0644 ~/.ssh/authorized_keys
Now add your public key in ~/.ssh/authorized_keys and save it
Copy the key from generated window
How to Login with PuTTY
Open PuTTY and Under Host Name (or IP address) enter your server IP or hostname as email@example.com or user@ipaddress
Next goto SSH tab on left hand side and click on + sign. Now click on Auth. Here in Private Key File for Authentication browser to your saved private key
Go back to session tab from left hand side options and click open. As you will now be asked for passphrase for the key file. Enter the key and you will be logged in into the server.
As you have completed the above step and you can login with your key file. Its time for disabling password authentication so that only key will be used for SSH connection.
Save the file and restart sshd
systemctl restart sshd
If you now try to login into the server without key file you will see the below error