Queens are essentially sexually mature regular bees. Workers are females that never receive sexual maturity. Queens are usually created when a hive is ready to swarm or when the old queen starts to fail and a new one is needed, a process called supercedure. You can tell which one is being created by where the queen cell is being built.
There are usually multiple queen cells made at the same time. When the virgin queens emerge, they will fight each other to the death. The winner will destroy any queen pupae that remain. This is the only time that honey bees fight each other, as workers of different colonies never fight each other, and can even be combined to save a weak colony. The winner will fly to a drone congregation area to mate. This also usually the only time that the queen will ever fly. She will mate with drones for several days and will never have to mate again for her entire life.
Queens are usually not that difficult to find. She is quite a bit larger than the workers and her abdomen will usually give her away. She will be surrounded by attendants, so if the frame she is on is not disturbed too much, you will see her move across the frame and a tiny gap between her and all other bees will form, creating a path where you can see her. Many beekeepers also mark their queens with paint so it is easier for them to find her.
Here is a series of videos of Stan Moulton talking about and interacting with the queens:
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