Minecraft: Windows 10 Edition was the former title of Bedrock Edition for the universal Windows 10 platform. It runs on Windows 10 PCs and tablets, as well as the HoloLens. Despite being a UWP app, it is not available for Windows 10 Mobile or Xbox One, so it is separate from the cheaper releases of Bedrock Edition on Windows 10 Mobile and Xbox One. (This means that XBL achievements are not shared between these platforms and buying the game on one of these platforms does not get you the game on the others.)
*DISCLAIMER - Saved worlds from JAVA edition are not compatible with this version. They are two different game versions! This is PC only version. Need to have Windows 10 as operative system to run/play.
How to activate key?
Open Microsoft Store (integrated Windows application). You can find it in Start Menu on your PC.
Sign in to your Microsoft account (Top right corner in the Microsoft store).
Click on the "See More" tab next to your profile icon (Top right corner).
On the drop down "See more" menu click on "Redeem a code"
After activation go to "Minecraft Windows 10 Edition" page and click "Download/Install"
Enter the code you want to redeem.
Click "Next" and then click "Confirm".
Once order is confirmed and the item has been delivered/received, there are no returns due to the product being a redemption key.