Windows 10 doesn’t ship with the software to play DVDs. If you want to make that happen, Microsoft thinks you should spend $15 (just under £10) on a Microsoft DVD-playing app from the App Store. Don’t do that.
It’s kind of a shame that there’s no built-in software to play DVDs on Windows 10 (one more thing to download for your grandparents!) but as anyone who’s wrestled with Windows Media Player knows, there are much better options out there anyway. Of the three people who have left ratings for the app on Microsoft's site, reactions range from "deinterlacer isn't the best, still leaves jagged edges", "way too expensive", to "Can't play vob files like window's media used to. Will play DVD disks and ISO's. Better than nada".