Amy, this question has been asked on here lots of times, I'll try to find some of the other answers. Basically your choice is really limited due to your age and employment rules - dog walking, car cleaning, paper round has been suggested in the past, also you can only do an hour or so on school days.
not easy unfortunately amy, as the insurance rates for your age are pretty stiff for businesses (like cafes/restaurants etc). Any local shops looking for cover.....?
The children around here come and ask me for jobs to do for money and I try to find them something. They wash and wipe the dishes, do errands for me and perhaps the dusting and mow the lawn. All these are nice and easy and can be done in a very short time. I have a set amount I give them - £1 for the dishes, 50p for an errand, £5 for mowing the lawn. It would be nice to offer your services to someone who can pay you but first of all you have to find someone and have to be willing to work.
What about making jewellery to sell to your mates? It believe it's quite cheap to buy the components. Or if you are a whizz on a computer, birthday cards, Christmas cards etc. Just don't spend too much on the initial outlay.
You can get a job oj but there are many restrictions such as how many hours you can work - a maximum of two hours on school days. If under 15 a maximum of 5 hours on Saturdays. Then there are other restrictions on the time of day they can work such as they cannot work before 7 a.m and they cannot work after 7 p.m. There are quite a few more which I can produce if you like. These are just a couple of examples.