You can either add your content or media in a presentation or drag and drop slides from Library Presentation to create your own CustomShow. 

You can also use any PDF, Image, Videos, Charts, Bar graphs and Tables in your CustomShow and give it build and animations.

You can also drag and drop Slides from other CustomShows to include them in your presentation and make a copy of it to make necessary changes in it. 

Check the below steps to create a presentation in CustomShow.