You will not need to create or register for an account to use Gizmos. Gizmos will use your Canvas log in to connect to your online lab assignments.
To connect your Canvas account to Gizmos, open the assignment labeled Gizmos Login from the Start Here: Course Resources or Launch Orientation module on the course modules page. 
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Once you see the page similar to the one below, you should be signed in. It will say "Your teacher has not yet added Gizmos to this class." That is fine - You just need to make sure your name is shown in the upper right corner indicating you are logged in. 
Now that you are signed in, you can access the various Gizmos activities. These assignments are normally titled something like "Gizmos: Name of Assignment" in your Canvas course. 
Access the lab by clicking the virtual lab links embedded in the Gizmos assignments in Canvas. For example, clicking the Gravity Pitch link in the screenshot below would open the Gizmos lab. 