An em dash is a common character in the writer's toolbox. Many word processing programs—such as Microsoft Word—automatically convert a double-dash into an em dash. However, it takes a little bit of work to use them in InDesign, where em dashes can be created either through the use of a hot-key combination or in the user menus.
Place your cursor in the location where you want to use the em dash.
Click on "Type" in the toolbar.
Scroll down to "insert special character" in the "type" menu.
A second menu will emerge from "insert special character." Select "hyphens and dashes."
From "hyphens and dashes," a third menu will appear. Select "em dash."
Simultaneously pressing Alt, Shift and the - (normal dash) keys will also produce an em dash.