There are several ways to add a PowerPoint file to Blackboard. This page will show you three options to share a PowerPoint to Blackboard.
Adding the PowerPoint as an attachment to an Item
How to save a PowerPoint as a Video
*If you have a voice over or have inserted video into a PowerPoint, the best option for showing this to students is to export it as a video and Embed it into Blackboard.
Sources and Relevant Links
Sample: http://its.syr.edu