If you already own Minecraft for the PC, you are eligible for the new Windows 10 Edition beta for free. Mojang has a post detailing how to get your free copy. This is a new version of Minecraft, coming after Microsoft purchased Mojang.
Windows 10 – Microsoft’s shiny new operating system – launches tomorrow. As announced at MINECON 2015 a few weeks ago it features a brand-new Edition of Minecraft. We’re calling it Minecraft: Windows 10 Edition Beta.