HELP?!

Hey guys,
So I am going on a traineeship with the police in 6 months. But if you want to join the police, you need to be in shape. And I am totally not. Now I know that being fit like being able to run 3 miles without any trouble takes time, so I'll be building that up in a few years 'cos I'm only sixteen.

Anyways I needs tips to loose weight FAST!

And another question, I've been told that if you skip lunch, you'll gain weight. Is that true?