Q. Normally Microsoft Word is by default double spaced. How can I make the default single spaced so that every new document starts out single spaced?

I was able to find the same question you had in Microsoft Community.  This was the solution that was stated there, hope this helps:

To change all future documents to single space click on the “Line and Paragraph Spacing” button in the “Paragraph” area of the Home page, and then “Line Spacing Options.” At “Paragraph” window change to “single” spacing and then click on “Set as Default” button at bottom of screen, and then check “All documents based on the Normal template.”