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. It is also found in Windows' command box, from Windows version 10. You run it from the local command line with the "ssh" command (example below). If you have a pre-10 Windows machine you can download and install a command-line ssh client from OpenSSH. Once you do, the ssh command will become available within the command box (Start/Run/cmd). ssh on any of these platforms are adaptations of the very same program so should be essentially identical to one another in features and syntax.
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:
ssh smith@sputnik.smc.edu
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.
On any Windows machine 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.
These are not the only ssh clients. In windows MobaXterm and Bitvise SSH client are both worthy alternatives. They have connection features beyond merely logging in, notably the ability to transfer files between local and remote machines, built in dual-purpose to one and the same program. By contrast PuTTY is a pure-play login client that doesn't transfer files; and FileZilla is a pure-play file transfer client that doesn't log in.
Have fun.