Microsoft PowerPoint is a presentation tool included with Microsoft Office. PowerPoint allows you to make interactive multimedia slideshows to present information. When you open a PowerPoint Presentation (.ppt, .pptx), the PowerPoint software is launched, but the presentation doesn't start automatically. If you want the presentation to start immediately in full screen mode and provide a more polished and professional experience, you should save it as a PowerPoint Show.
PPTX PowerPoint Presentations are different than the PPT version in that they use the Microsoft Office Open XML format. The Open XML format makes it easy for other programs, such as OpenOffice.org, to read PPTX files (and other Open XML file types). The Open XML format was introduced with Microsoft Office 2007.