As a supply teacher there are a number of differences compared to that of a permanent teacher. Supply teacher roles are there to allow schools to take on members of teaching staff on a temporary basis. It may be that the school requires cover for sick leave, maternity leave or for cover when a teacher is going on a course. Sometimes supply work is only for a day or so and other times it can last months.
As a supply teacher you will find that some things are better than teaching in a permanent position but other things are worse. For example, the pay is often better for supply teachers than permanent staff but you may not be guaranteed 5 days a week of work. Yu may not have to take on responsibility for planning and preparing the work for a class, which can take a huge part of the stress away from the job.