SSH ("Secure SHell") is a protocol for securely accessing one computer from another. Despite the name, SSH allows you to run command line and graphical programs, transfer files, and even create secure virtual private networks over the Internet.
To use SSH, you will need to install an SSH client on the computer you connect from, and an SSH server on the computer you connect to. The most popular Linux SSH client and Linux SSH server are maintained by the OpenSSH project.
Make sure you have a strong password before installing an SSH server (you may want to disable passwords altogether)