Finding a job when you're under 25 is hard these days, and under 18's have it even harder! Without having experience, you have a lot to prove to a potential employer, which is why most schools are part of the work experience programme that operates nationwide. From this, you gain experience of a real working environment, and if you do a decent job, you get the benefit of having met a manager who can give you a work reference in the future.
This absolutely should be included in your CV. Have a look at the templates and samples here for further guidance on how to constuct the bones of the CV.
Got no work experience? Ask one of your teachers for a letter of recommendation and include information in your education section about anyextra curricular activities where you have worked in a team, had leadership, or have developed certain skills. My friend landed a job in a call centre aged 17 with no experience as a German speaking operator, because she did the British Airways Language Flag award in German. Underestimate nothing.
Good luck with your CV and job hunt!