2. What does it do?

Ssh (Secure Shell) is a program for logging into a remote machine and for executing commands in a remote machine. It is intended to replace telnet, rlogin and rsh, and provide secure encrypted communications between two untrusted hosts over an insecure network. X11 connections and arbitrary TCP/IP ports can also be forwarded over the secure channel.

You can also use secure transfer programs, scp and sftp to replace ftp.