In DECS Labs and RDS simple ssh connections are facilitated by the software PuTTY. PuTTY is free and open source. You may want to look into X2Go for connections to the DECS Compute Servers requiring a GUI/Graphical User Interface.
ssh (Secure Shell) is a utility to login to another computer over a network, to execute commands in a remote machine, and to move files from one machine to another. This is also used quite a bit for checking email. It provides strong authentication and secure communications over insecure channels. It is intended as a replacement for rlogin, rsh, rcp, and Telnet.