How to Work with PowerPoint Web App Presentations
In Office 365, PowerPoint Web App is a component of the Office Web Apps services available in both the professional and small business plan (P plan) and the enterprise plan (E plan). In the professional and small business subscription plan, you create a new presentation with the PowerPoint Web App as follows:
Click the PowerPoint icon from the portal.
Enter a filename at the prompt.
After you click OK, the web app will launch and you can start editing your presentation on the browser. Your file will be saved in the default team site document library called Documents.
In the mid-size businesses and enterprise plans (E plans), there are no web app icons on the portal. Creating a new presentation requires opening the PowerPoint 2010 desktop application. After creating the document, add it to your document library so that you and others can view and edit the presentation by using the PowerPoint Web App.
Alternatively, you can add the PowerPoint content type in your document library so that you can create presentations right from SharePoint Online.
Editing presentations is as easy as clicking the Edit in Browser button from the Reading View when your document is loaded on the page.
There is no Save button in the PowerPoint web app — your file is saved automatically.
To close an open presentation, click File from the menu in the Editing View and then click Close.