To become a qualified accountant you must undergo a period of training in a training practice which has been authorised by one of the professional accountancy bodies such as the ICAEW. Training generally takes between three and five years, during which time you will study for the professional body's exams and gain practical experience. The training practice will pay you during this period and will allow you study leave so that you can complete the course.
Once the training is satisfactorily completed, you will have gained a professional qualification and become a member of the professional body. After a further period of work experience you can apply to the professional body for a practising certificate so that you can set up in public practice. You will be entitled to use the title Chartered or Certified and you will have to comply with the rules and regulations of the professional body.
If you want to do audit work you'll need to obtain a recognised audit qualification. This can only be awarded by a Recognised Qualifying Body like the ICAEW or ACCA.