Secure SHell is a simple but secure way of accessing a computer remotely over the command line.
SSH has two parts, a server and a client. The server by default listens on TCP port 22.
To use SSH from Windows you’ll need a client. I suggest PuTTY: https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
On Linux or Mac, ssh (at least as a client) is built in and can be used directly from the terminal.