Depending on your location, state, etc. Will determine how long you will need to go to school. In some states it is 1000 hours of Cosmetology School, in other states it is 1500 hours of Cosmo. School.
Once you finish school, and have graduated, you will need to pass a "State Board Licensing Exam"; two parts, a written and a practical. A written exam is a multiple choice exam, with random questions related to everything you learned in school. Sanitation, hair, skin, nails, etc. And the practical is a hands on exam showing you can perform what you learned in school. You bring in a live model and are given timed increments to perform tasks, hair, skin, nails, make up.
Once you take the State Board Exams and pass both parts, you will then get a license by the state. Then, you can work in a salon and have customers/clients.
I recommend looking into Cosmetology School either a private school or a vocational high school. You can take a tour and ask questions. And also, if you have friends or family members who know people who have or are working in the business, see if you can talk to him/her directly as well. Good luck! 😀