To redeem a Steam key and play, you will require a steam account and the game client, the Steam game client can be downloaded here: https://store.steampowered.com/about/
And you can create an account here if you do not already have one: https://store.steampowered.com/join/
To redeem your game keys, follow the below steps:
- Launch the Steam client and login to your Steam account.
- Click the games menu.
- Choose activate a product on Steam.
- Follow the onscreen instructions to complete the process.