That means that you have to TELL it what to do by typing commands in at a terminal or terminal emulator. It is also a multitasking, multiuser operating system, and some of the commands reflect this. All of these things make using it a bit different than using a Macintosh or Windows machine. Practically speaking, it is easier to do something once using the Graphics User Interface you'd find on the Web, Mac, or Windows, but it is much easier to automate repetitious tasks using command lines. It's also much easier to write a command line program than a GUI program, and if you dig down underneath the various web sites and email servers at bottom what you'll usually find is a command line program.
Some programs make use of the keypad area on the keyboard.
They have defined commands for each button press there. For instance, the editors do this, as does the MAIL utility. For these to work, your terminal emulator must be configured correctly, in particular, it should emulate a VT100 or VT200 series terminal, and should communicate this to Seqaxp when you connect. This will list the various help categories, and at the bottom, the available help libraries. Move through this information by entering words at the prompts, or by specifying the full path at the command line.