SharePoint Online is one of the core services available in Office 365 and it shares many of the same features you find when SharePoint is deployed locally or when purchased by a hosting providers. (If you need a good introduction to "what is SharePoint" here is a very good video.) One of those features is known as a "slide library".
Slide libraries are a really interesting feature which allows you to work with PowerPoint slide decks stored in the cloud in a unique and potentially very useful way. Note that Slide Libraries are not available in the Office 365 for the small business and professionals version of Office 365. So, before you get started, you will need Office Professional Plus or Enterprise to publish to slide library, however, other versions of Office can use a slide library as a source once it is published.
PowerPoint slide decks are quite different than say, a word document. If you write a paper that's ten pages long, you generally need all ten pages. In other words, each page is not a standalone unit. You wouldn't typically assemble a new document by picking some of the pages from the old document and adding new content. But with a slide deck, each slide is a complete object. Each slide represents a talking point or concept and can have unique speaker notes, animations, and media built in.
If you've worked with slide decks much, you know that a good slide can be re-used in number of presentations. In my own work, I often use the same core slides for topics like "Office 365 Overview" and add specialized content to suite the particular audience or topic at hand. Over time, this results in decks existing on your system with a lot of redundancy. Therefore, if you want to update a slide that appears in several decks, you could be looking at quite task to locate and then update each deck. The more people you have in an organization using PowerPoint decks, the bigger the problem.
A SharePoint slide library is designed to solve this problem. When you upload a PowerPoint deck to a slide library, each slide becomes an individual entry in the library. To build a new deck, just click on the slides that you want and select Create a New Deck. This will automatically assemble the new deck from the selected slides. But even better - you can link the new deck to the slide library stored in SharePoint Online. So when you open the linked deck, it will check with the slide library to see if any slides have been updated and if they have, it will update the slides automatically. In this way, you keep a "master" set of slides in the cloud and all the linked decks stay updated automatically.
First you need to have a slide library available for use with your SharePoint site. If you do not have permissions to create libraries, you will need to contact your SharePoint service administrator to add a slide library and setup permissions so you can write to the library. Creating a library is simple. You can follow the step by step instructions in Office.microsoft.com.
When you create the library, you have the option of enabling version control. This is a simple but powerful feature that causes SharePoint Online to update the version number associated with each slide when it is updated. In this way, you can tell when a slide is updated and even restore to a previous version of a slide if necessary.
After your slide library is created, browse to the library in SharePoint Online and select Upload | Publish Slides. Browse to a slide deck and select the deck. You can then select which slides you want to publish to the library. When everything is selected, click Publish.
PowerPoint will open automatically and publish the selected slides to the library. Now, when you browse to the document library you can select the slides you want to use, and click Copy Slide to Presentation.
The next thing that happens is where the magic happens. You are asked where to insert the slides (a new presentation or one you have open) and you can enable "Tell me when this slide changes"
You can then save the deck locally, but the next time you open it, PowerPoint can check the slide library to see if there are any updates.
In addition, you can right click on any slide in PowerPoint and manually check for updates at any time. Of course, you can still take advantage of SharePoint Online features such as checking slides out, adding workflow email alerts when changes are made, adding custom fields, and many other SharePoint Online features related to libraries.