Microsoft launched Windows 10 today, which means that Minecraft: Windows 10 Edition's beta is now available. As developer Mojang announced during Minecon 2015 earlier this month, the Windows 10 Edition Beta will be available free to the 20.3 million people who have bought the original PC/Mac edition of Minecraft, and Mojang detailed the process in a blog post yesterday.
The steps are pretty simple. If you own Minecraft, log in to your Mojang account, where you should see a "Redeem" button. (Mojang said in an update today that it is "still rolling out" the button, so don't panic if it hasn't shown up yet.) After hitting Redeem, you'll have to sign in to your Microsoft account and follow the instructions to claim your free copy of the Windows 10 Edition Beta.