The school will sponsor you once they have accepted you for a post. Unfortunately you will not be able to leave the country without the permission of your sponsor. This means that if you don't like the the job and want to leave you will need the cooperation of the school who at that time may be desperate to keep you on. I've met a teacher who was not allowed to leave at the end of last year and she will have to work another year before her school agrees to let her go.