ssh is a program that can be used as a remote terminal emulator. With it, you can achieve a character-mode (non-graphical) connection to a shell on another machine and conduct a command session.
You need to have an ssh client program on your end. If you have a linux or Mac machine one is probably already installed there. You run it from the local command line with the "ssh" command (example below). The target machine must have an ssh server on it, and you must have an account there. Suppose your remote user account name is "smith" and the remote machine is "sputnik.smc.edu". Then the command by which to make the connection and gain a session on sputnik.smc.edu is:
The result should be a password prompt (presented to you by/from the remote machine) where you can log in as smith if you supply smith's password.
If you have a Windows machine there are two widespread ssh clients. First, you can download and install a command-line ssh client from OpenSSH. Once you do, the ssh command, with the same features and syntax as in the linux/Mac world, will become available within the command box (Start/Run/cmd). Second, you could install the graphical ssh client PuTTY. When you run it you get its main window:
Type the IP address or domain name of the target computer in the "Host Name" field. Press the "Open" button. The first time you do this you'll get the following friendly warning. Press "Yes".
A new character-mode window opens prompting you to log in. Give your user account name, then when asked the matching password.
Note that with command-line ssh you supply the user account name in the original command, along with the target machine name. With PuTTY by contrast you only supply the target machine name; you'll be explicitly asked for the user account name afterward, by the remote machine, once you're connected to it.
A PuTTY alternative I recommend is portaPuTTY. Its distinction from regular PuTTY is that you can carry it around on a USB flash drive and run it on different Windows machines you may use. (Regular PuTTY installs on a particular machine to which it is then confined.) Download the provided file onto your flash drive. Unzip it there; it will create a folder name "portaputty". Within it is "putty.exe". Manually run it by double-clicking on it.