Abyssus | GL

Launch the Steam client and sign in to the account you want to add the game to — the key is permanently bound to the account.

In the client's top menu, open the "Games" section.

Select "Activate a Product on Steam…" and follow the activation wizard's prompts.

Enter the key you received and confirm — the game will appear in your library and become available for download.

Via browser: open store.steampowered.com/account/registerkey and sign in to your Steam account.

Paste the key into the field on the page, accept the user agreement, and click the activate button — the game will be bound to your account and appear in your library.