It's YouTube for PowerPoint. Really! In Slideshare you can upload Upload powerpoint content and converts to a Flash format that easily embedded in other web sites. The slide files it take include not only PowerPoint, but PDF, and Open Office (it also allows you to upload various document and video formats to share in a similar fashion).

The storytelling aspect comes in when you link a slide deck to audio, what Slideshare calls a "slidecast". You can upload an mp3 audio file (or link to it if it is already on the web). Once connected, you use a screen that provides the audio in wave form and use the built in tools to sync what part of the audio should play for each slide.

Slidecasts have been discontinued as of April 30, 2014 http://blog.slideshare.net/2014/02/07/slidecasts-to-be-discontinued/ so slideshare is only good for putting together images and text.