Click through these slides for the best free PowerPoint templates from hundreds available on Microsoft's download site.
It is important to notice whether the template was created for a version of PowerPoint compatible with the one you use (2003, 2007, 2010, or 2013). In general, you can use templates earlier than your version but not later.
For example, this Animated Floating Flower Petals Presentation Template for Microsoft PowerPoint is for Microsoft Office 2010 so unless you have a 2010 version or later you may not be able to download this particular template.
Whether you use PowerPoint all the time or are jumping in as a new user, templates are wonderful tools. They can be customized element by element, including color themes. Finding one that is already close to what you want can save you time.