If you have an SSH key, you have to load it using the pageant.exe program which can be downloaded from this URL.
After the pageant.exe download, start the program and load your private key in it. If you have generated your key with a passphrase, you will be asked for it.
Then you should start putty.exe and enter the connection details in the Session category:
- Host Name (or IP address) - here you should enter the host/IP to which you wish to connect;
- Port - the port for the connection - here you should type 22 (unless you have changed it, which is advisable);
- Protocol - here you should select SSH;
Once you enter the correct details, click on Open to establish the connection. You will be asked for a username; once you type it, you will log in your account via SSH.