I'm the same as you! 17, and struggling with disordered eating. I've never known the 'right' way to eat, or what the 'right' thing to eat is. Some days, I eat nothing. Some days, I binge like mad. Some days I eat about the average amount.

I'd say that a 17-year old girl should be eating around 2000 calories. 6 small meals a day is best, or 3 main meals if you prefer.
Breakfast - cereal or toast (or both, if you want) or fruit and a drink
Snack - whatever you want (fruit, snack bar, crisps etc)
Lunch - meat with vegetables, or for a packed lunch, a sandwich, snack bar, fruit, and a drink
Snack - fruit or snack bar
Dinner - meat with vegetables (if you didn't have that at lunch) or soup/pasta/beans on toast/salad etc.

Make sure you eat plenty of fruit and veg if you can. Try to stay away from processed foods such as ready meals, and salt. Drink plenty of water (8 glasses) and make sure that you get at least 7-8 hours of sleep at night, otherwise, your appetite will increase.
I'd also advise to not start with a diet right away - try to get 'normal' eating mastered first, and take it slowly from there. If you want to diet after you've managed to stay consistent in your eating, message me and I can help you

Keeping a food journal helps too - write down your feelings when you want to binge/purge, and write down what you eat and when. And don't forget to do at least 30 minutes of exercise every day! Good luck!