I assume that the question refers to the PC (I don't know for XBox). 1. you need the Microsoft Store, which should be pre-installed under windows. 2. click on the 3 points in the upper right corner. 3. click on the point "Redeem code" or similar. 4. a window should open where you can enter the code. 5. if you were able to do this successfully, the product should be bound to your Microsoft account and you should be able to use it. 6. i.e. there will be an install button somewhere that will start the installation. From then on it should be self-explanatory.

We only distribute the code, which you should redeem via Microsoft to get the corresponding download.