When you want to quickly insert a horizontal line into your Word document instead of going through the Borders and Shading dialog box in the Ribbon here is a keyboard shortcut to save you time.

In this example I put a simple divider line between two paragraphs in my document.  Just type 3 dashes — and hit ‘Enter’ immediately after.

You can also change the type of horizontal line you are inputting by changing up the characters you use for this short cut.  In the following Word screen shot the green highlighted area shows the various horizontal line breaks possible.  Three asterisks***, three underscores___, three equal signs ===, three pound signs ###, and three tildes ~~~

For more fun features, check out this Microsoft Word Easter egg, or this undocumented Word feature.