Queen rearing is the production of mated queens for use in the apiary or for sale, and involves breeding and selection of suitable queen mothers and drones to produce bees that possess desirable characteristics.
The underlying concept of queen rearing is to get the highest number of the best quality queens from the least resources.

Where do queens come from?

A queen is made from a fertilised egg, exactly the same as a worker. It’s the feeding that is different and that is only different from the fourth day on.

If you take a newly hatched worker egg, and put it in a queen cell (or in something that fools the bees into thinking it’s a queen cell) in a hive that needs a queen (swarming or queenless) they will make those into queens.

Timing of Queen Rearing.

In general, the best time of the year for producing good quality queens is when nectar and pollen are abundant, and there are enough drones available to ensure successful mating.

In the UK, this is the period between mid-spring and mid-summer – basically when bees might be expected to swarm.

Raising queens late in the season is not recommended as emerged queens may not have a good chance of mating; queens that do not collect a sufficient amount of sperm at mating time are bad layers and will be superseded by bees.

Queen rearing is a straightforward process, and is an essential part of beekeeping.
See the links below for detailed information.