1) Go to this page: https://www.minecraft.net/en-us/redeem and log in to your Microsoft account or sign up to your Minecraft account.
2) Create a gamertag then click "Let's Go"
3) Enter the product key assigned to you that was visible on the order summary page or sent to your email then redeem code.
4) Claim the game.
5) Set up your profile then proceed to the next step.
6) Download the launcher then install the game. (If you accidently close this page then go here).
7) Find and open the game on your device then login to your account to start playing.