Not sure where you are stuck exactly.
When you bought the game from us (Jul 9, 2019) we sent you a Steam Activation code by email, and it may also be visible here:
Click on Manage for the relevant game, the key should be visible in there.
THEN You must have, or create, a Steam account and install the Steam Client application from their website.
Steam is the ultimate destination for playing, discussing, and creating games.
"Install Steam Now"
Just paste your Steam Activation code into the +Add a Game area of the Steam client application, and the game will be available in your Steam Library in that Client to download and install. You can also do this directly on the Steam website
Does that help?