Cockerels are male chickens that are less than 1 year old. They are not referred to as roosters until they are one year old. It would be like calling a two-year-old toddler a man!
Hello and welcome to BYC! :frow Glad you joined.
They don't do this automatically. Not all hens will become broody. It's a hormonal thing. You have no control over it happening or not.