To download the Add-In go to the download page and select the appropriate PowerPoint Add-In for you. Global, Hosted, and or Demo.
Open the file in PowerPoint (enabling editing and macros if requested),
and save it as a PowerPoint Add-in (.ppam) file type. PowerPoint should default to the special Microsoft folder used to hold your PowerPoint Add-ins (record the path if it is different).
Close the add-in PowerPoint file and open a blank PowerPoint presentation.