You will find the DMG (disk image) file on the download page of the MuseScore website. Click on the macOS link to start the download. When the download is complete, double-click the DMG file to mount the disk image.
Drag and drop the MuseScore icon to the Applications folder icon.
If you are not logged in as administrator, macOS may ask for a password: click Authenticate and enter your password to proceed.
When the application has finished copying, eject the disk image. You can now launch MuseScore from the Applications folder, Spotlight, or Launchpad.
Note: As of macOS 10.15 "Catalina", the system has to be told to permit MuseScore to be allowed to access user parts of the file system. The first time you use it on Catalina, it will ask you if you wish to permit it; of course, answer "yes", but if you bypass this by accident, you can set it via System Preferences > Security and Privacy > Privacy > Files and Folders. Unlock with your Admin credentials, then navigate to MuseScore (whichever version(s) you have and want), add it or them to the list of apps, and select "Documents" and "Downloads" folders, or as you prefer.
Simply delete MuseScore from Applications folder (Admin access will be required to do that, however).
You can deploy MuseScore to multiple computers with the "Copy" feature of ARD. Since MuseScore is a self-contained application you can simply copy the application to the '/Application' folder on the target machines. It is also possible to install multiple versions of the application as long as their names differ.