You need to save it as a ppam AddIn (you would need to add XML to create a ribbon button to run it.
Simple example
on our site here of making the ribbon. You would need to save the file as a ppam and then go to File>Options> AddIns> PowerPoint AddIns > Add New to enable it.
Much harder than Excel! We also have a free downloadable "kit" that will walk you through having up to four macros on the ribbon. Still a learning curve but it should help.
Download here