MuseScore -- Index -- Create new Score from Scratch

Create new Score from Scratch
The menu entry <Score/New> create an empty new score. First you have to populate the empty sheet with instruments and then you can add empty measures. Next steps are usually: set clef, set key, set time signature
Create new Score from Template
<N> popups the <Template> menu. Select a template and click <Ok>. This is the simplest way to create a new score. Note that template files are normal MuseScore files stored in the template folder.
Create new Score with the New Wizard