PuTTY Version 0.7
PuTTY is a client program for SSH, Telnet, and Rlogin network protocols. All of these protocols are used to run a remote session on a computer, using a network.
PuTTY implements the client end in the session: the end where the session is displayed, not the end where it runs. A simple example: run PuTTY on a Windows machine, and instruct him to connect with (for example) a Unix machine.
PuTTY opens a window. Then, anything typed in the window will be sent directly to the Unix machine, and everything that the Unix machine sends back is displayed in the window. So, when working on a Unix machine it looks as if the user is sitting on his console, when in fact he is sitting somewhere else.