Testers may leave feedback for you at the conclusion of their test about their experience. They'll likely comment on what worked, what didn't work, and unexpected behaviors that they experienced during their testing of your application. You can either Accept or Delete any of the tester feedback.
If the tester feedback were accepted, it will appear under the section called Feedback to take action on, which acts like a to-do list for your team. From there, feel free to Archive the feedback after you've taken action on them.