For the most part, yes, in order to score on outcomes, you have to add them to a rubric, and then add that rubric to your assignment, discussion, or quiz. The only exception is that you can add an outcome to a question bank without first putting it on a rubric.
In the guide How do I create an outcome, there is mention of how/where to use an outcome. @dtod is there a place where you'd like to see the details about outcomes in our guides? You're encouraged to use the "Leave Feedback" button at the bottom of any of Instructure's guides! Our LMS Documentation Team will review the request and your feedback.