A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
The best answer is probably: Don't.
PowerPoint's drawing tools have improved tremendously over the years but the curves are still a little weak, and there's no automated tracing capability at all.
If you have Corel Draw, use it instead. It's got very capable/flexible tracing options. Or google "trace image to vector" (without the quote marks) for tutorials for other programs you might have (Illustrator, Photoshop) and online/desktop tracing tools.