Start Parallels Toolbox. If you haven't signed it yet, you will see the registration window. You should either sign in to your existing account or create a new one.
After you log in or create an account, you will see the activation window.
Enter your activation key for Parallels Toolbox, or a key for Parallels Desktop copy that includes Parallels Toolbox, and click Activate.
Your copy of Parallels Toolbox will be activated.