Putty is an ssh client app to connect to a remote server in a secure way.

Developed and primarily maintained by Simon Tatham, PuTTY is an open-source application that makes use of network protocols like Telnet and rlogin on Windows and UNIX platforms in conjunction with an xterm terminal emulator. Over a network, PuTTY makes use of all the above protocols to enable a remote session on a computer. It is a popular tool for text-based communication and is also a popular utility for connecting Linux servers from Microsoft operating system-based computers.

Passphrase: A passphrase on a private key is an extra layer of protection. Even if your private key is discovered, it can't be used without the passphrase. The downside to using a passphrase is that it makes automation harder because human intervention is needed to log on to an instance or copy files to an instance.

Follow this documentation to connect to an EC2 server using PuTTY: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/putty.html