Whether you want to lose weight or put on muscle diet is key. Both weight loss and putting on muscle are 80% diet,
with exercise being just a small portion. The /r/Fitness FAQ has a very detailed description on diet and nutrition.
The basic overview is this: use an online calculator and find your TDEE (Total Daily Energy Expenditure - basically
how many calories you burn a day just being alive and working), add 500-1000 calories if you want to put on weight,
subtract 500-1000 calories if you want to lose weight. Eat this number of calories every day. If you just wish to
maintain weight, just eat at maintenance (your TDEE). It's that simple.
500 calorie difference equates to 1lb/week and 1000 calories equates to 2lb/week. It's not recommended to go above that
for either gaining or losing weight. It is also recommended to try to get 1 gram of protein per pound of your bodyweight
a day. There is some debate what the exact amount of protein needed is, but this goal will do as a good target.
It is also highly recommended to track calories. You can use any calorie tracking method you want, some popular ones are MyFitnessPal,
Lose It!, FitDay, My Plate, with most of these websites having smartphone apps. You may find a food scale will be
helpful in determining food servings. Cheap ones run around $20 to $30 and do the job just fine.
Using these methods you can burn fat or bulk up to gain muscle, just like you could with traditional weightlifting or cardio.