Watch people try real tasks
A team might ask someone to find an invoice or change a delivery address, then watch what they do and where they hesitate. They can use the live product or a prototype. The participant is helping test the design, not being judged.
A researcher may guide the session, or participants may work through the tasks alone. Teams choose people who might use the product and note what works as well as what causes confusion.
What a few sessions can show
A few sessions can reveal design problems, but cannot show how common they are. Analytics can show where people abandon a task; larger studies can show whether the same problems recur. Teams include people with different abilities and devices, then make changes and test again.