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.
Reza has explained some options to check if you need to remove a background on a *slide*. But if you've inserted a picture and want to remove the background from it, that's a different matter. In the desktop version of PowerPoint, there are tools to help with this. The phone/web/tablet versions of PowerPoint lack many of the features of the desktop version and unfortunately I don't have the Android version to check.
Do you have access to the desktop version?