A hairdresser's job is to organise hair into a particular style or "look". They can cut hair, add colour to it or texture it. A hairdresser may female or male. Qualified staff are usually called "stylists", who are supported by assistants. Most hairdressing businesses are unisex, that is, they serve both sexes, and have both sexes on their staff.
Qualifications for hairdressing usually mean a college course, or an apprenticeship under a senior stylist. Some aspects of the job are quite technical (such as hair dying) and require careful teaching.