Even when a teacher has finished getting their degree, they are by no means ready to be a qualified teacher. Before they can really start their career they still need to undergo teacher training, where they get to truly experience life and work as a teacher in their chosen environment.
Teacher training varies from place to place, with the school or university the trainee is placed in playing a big role in their education. Their role usually consists of being either a stand-in for other teachers, or as a teaching aide to help teachers and students in class.
After a trainee has finished this part of their training, it still isn’t done. After they’ve done that part, they need to enter their NVQ period, which is a lot like a probationary period, where they will have to work like a teacher for a full year, before they receive their qualification and have the right to work where they choose.