Workout:
Lifting weights if you want buff up, this varies for everyone, I'm sure that if you go to a gym they can advise you on what to do and how to do it.
If you strictly want to go outdoors and dont really care for being buff, like MJ said, run/ride bike and maybe tennis.

Food:
Lots of protein, for example: chicken, eggs, fish, milk and protein shakes/bars.
Generally you need about 2 gramms of protein for every kilo you weigh to grow. I weigh 71 kilo's so I usually eat/drink around 140-150 gramms of protein a day.