Hi  @mwalton  Welcome to the Canvas Community.  It depends on exactly where you mean when you say "in a module" but I can tell you that the general solution to this is--while holding down the SHIFT key on your keyboard--tap ENTER on your keyboard.  That is what us old fogeys of a certain generation may call a "soft return" (from our word processing days when we didn't want a new paragraph in WordPerfect or Word!) and what the current generation would call a line break.  Be aware this will only work within Canvas' rich content editor, generally.

This is fairly normal in many web-based editors, because they are trying to adapt to the wonderful world of HTML tags.  Typically, hitting ENTER will generate (in the underlying HTML) the paragraph tag (or <p> tag).  We will see this as double-spacing when compared to a text-based document, or--,more accurately--a blank line between paragraphs.  Using the SHIFT-ENTER routine will instead generate a </br> tag, or a line break tag.  

All technicalities aside, however, be aware that--depending on your user's choice of browsers (or smartphones!) while using Canvas--there are often very good reasons for that empty space between paragraphs, including readability.  My own preference is to avoid creating a line break unless there's a really good reason for doing so, but since I don't know enough about what you are trying to accomplish, I'll just shut up now while I'm somewhat ahead! 

I hope this helps a bit, Maureen!