You can enter MEL commands in the Command Line or the Script Editor. The Command Line can only accept single line MEL commands, while the Script Editor provides a method to input multiple MEL commands and view the results.
By default the Command Line is in MEL script entry mode. You can change the mode by clicking on the text in the lower left hand corner. For this lesson, ensure the Command Line is in MEL script entry mode.
In the Script Editor, the Enter (Windows and Linux) or Return (Mac OS X) key above the Shift key does not execute a command. It starts a new line so you can type several commands before executing them.