Ctrl / clic : hold down the Ctrl key while clicking the mouse.
Ctrl + a : hold down the Ctrl key and press the a key.
The ⌘ key is called "Command" and abbreviated Cmd.
To open a contextual menu :
Screen images used in this documentation display either the MacOS and Windows version of the software. In most case the functionnalities and appearance are equivalent on these two platforms.
Also note that most screen captures are from the French version of Musique Lab 2, so texts are generally different in the English interface.