Adding content to your Engage interaction is as quick and easy as filling out a simple form. There's a place to enter and stylize your text, a place to add an image or a movie, and a place to import or record audio.
See these tutorials for details:
Adding or Removing an Intro or Summary in Your Interaction
Stylizing Text in Your Interaction
Adding Hyperlinks in Your Interaction
Adding Images or Movies to Your Interaction
Adding Audio to Your Interaction