A brief history of computer audio and MusE
To quickly summarize over a decade (two decades!) of open source development:
In the early days of 2000 Werner Schweer released the first version of MusE as the package muse-0.0.1.tar.gz. In it’s first few releases (actually not few, Werner relentlessly churned out new releases) MusE was only a midi sequencer. The target was to create a fully fledged midi sequencer for the Linux operating system. Over the years audio was added among with other things implemented and sometimes abandoned. Today MusE is a stable and feature rich music creation environment which strives to encompass most of the music recording process, creation, editing, mixing, mastering.
CTRL refers to the control key on the keyboard, e.g. CTRL+C means to press and hold the control key while pressing the c key. Make sure you know where you have it so you won’t accidentally lose control (bad jokes are the best jokes, so say we all!).
SHIFT refers to the shift key on the keyboard, see above for usage
ALT refers to the alt key on the keyboard, see above for usage
$> is used as a generic definition for a terminal prompt. When the manual lists a command that shall be typed, the prompt is not part of the command.
Keys are always referred to in bold uppercase, e.g. A. For instance SHIFT+A for the key a pressed together with the shift key.
Sometimes terminal examples are written tabbed in with a fixed font to visualize more closely what something looks like on the screen. E.g.