In a usability testing session, the team observes real users interacting with the product. Typically, a facilitator sits with a user and asks her to complete tasks and explain her thinking as she goes. The team sits in a separate room and observes the testing by video.
A usability test is not a focus group; it's focused on what the user thinks and does in the real world.
A usability test can be run on an existing product, a prototype, or even a competitor's product! The prototype could be working code, or it could be something as simple as a few clickable images. Test early and often to create products that delight users and solve real needs.
Something that's obvious to someone who has been working on a product might be confusing to a user.
What we think users need might not be what they actually need.
What users think they need may not be what they actually need!
Usability testing can help answer questions such as, "Are we on the right track?", "What problems do we need to solve?", or "Which features should we build first?"
With early feedback from real users, teams can avoid sinking time into a feature that's confusing or not useful.
Watching real people use a product builds empathy and understanding - which is why it's important to include the entire team.
Check out these great links which can help you dive a little deeper into running the Usability Testing practice with your team, customers or stakeholders.