Many students have the opportunity to go on a work experience week or possibly even two weeks when at secondary school. This is usually done in year 10 and then it may be offered again if you choose to stay in education. Some college courses and uni courses also ask that you take part in a certain amount of on the job training to allow you to gain experience in the industry.
When choosing where you want to go for your work experience, think about what interests you and what you may wish to do as a career further down the line. If for example you are set on being a teacher, then why not contact a few local schools and see if they have any work experience placements that they would be willing to offer you. If you are torn between two careers then you could always ask your school if you would be able to do one week at one place and then a second week at another place.