After you have redeemed your product key, it should be associated to your Microsoft account.
To install it, just click the button Install in your Office account.
Follow the steps described there, and begin with the installation process. The installation program may take a short while to download and install the program. It make take a while.
Once it is installed, open one of your newly downloaded Office programs, and login with the email you used to redeem the product, if the program requires it.