The Users tab enables you to diagnose issues for specific users, by helping answer questions like "which experiment group was this user in?" Or "when did the user first see this feature?"
How the Users tab works
When you enter the User's tab, you specify which user's data to load and pick a date range (1-2 days is best). The query takes between 2-10s depending on the amount of data you have. If you click on the timestamps in the Log History you can see additional details for this event on the right.