Unity Live Help uses an algorithm to match you with the best available expert; somebody who specialises in the area you need help with. It's important that both you and the expert are confident about the expert's ability to help you, and for you both to have realistic expectations. For this reason, each session comes with a five-minute "grace period", during which time you and the expert can discuss your problem and decide whether or not you want to work together on the problem.
If you decide to continue working with the expert, then you pay for the first five minutes, and each subsequent minute of the session.
If you decide not to work with the expert, then the initial five-minute consultation is free, and the session ends after 5 minutes.
See What happens once I am connected with an expert? to learn more about how to convert a session to a paid one.