Make sure you have the MakeMusic Finale software installed on your computer. If you don't, you'll need to purchase the software and install it. There is also a trial version of the software available on the company's website (see the link in References).
Open MakeMusic Finale. Click "Start" then "All Programs." Select the "MakeMusic" folder then click on the "MakeMusic Finale" icon.
Click "File."
Click "Open." Select the .MUS file from your computer's hard drive. The contents of the .MUS file will now open in the main MakeMusic Finale program window.