Chickens are very social animals, and are best kept in small groups.
Within any group, a hierarchy or ‘pecking order’ will develop. This isn’t a problem, unless one chicken is persistently being bullied by the others. Adding new chickens to an established group can be problematic as this can upset the balance. In both cases you will need to protect any chicken that seems to be suffering physical harm from others. If necessary seek advice from your vet.
Adult males (cockerels) aren’t essential if you would like to produce eggs, as hens will happily lay without them, although these will never hatch. If you are thinking about getting a cockerel, bear in mind that they can be noisy and are likely to upset your neighbours.
If you have to separate a chicken because it is poorly or being bullied by others– keep it within sight of the main flock, otherwise it may be bullied even more when reintroduced to the group.