While working in the command line console, not running X Windows, you suddenly need access to another shell to do another task. You don't want to quit or halt the current application. What might you do to run both your other functions in a shell while still running your current application?

You can press ALT-F2 or CTRL-ALT-F2 to open an alternate console screen and access a new shell session.

Explanation:

Pressing ALT-F2 or CTRL-ALT-F2 will open an alternate console. You can use this console to perform other tasks without stopping the program running in the first console screen. You can switch back by pressing ALT-F1 or CTRL-ALT-F1.

So you do the above trick to run both your other functions in a shell while still running your current application.