Jona wrote:I am pretty skinny, I always eat a lot of shit like candy and McDonalds and also good, regular food.
But I never seem to gain any weight!
What should I do???

there are two types of bodily weight that can be gained or lost. Fat and muscle. The fact that you do not get extra fatty tissue due the things you eat is a blessing, many people would love to be in your place. It's just your metabolism that burns away everything fast.
You should try eating 4 - 7 meals a day, mostly rich in protein ( chicken breast, turkey breast, egg whites etc) and carbohydrates (bread, spaghetti, rice etc). This COMBINED with a workout schedule will get you results, maybe not fast, but they will come.
The only problem peoplw with your metabolism rate seem to have, is that they cannot get too bulky and muscular as easy as the rest. But as long as you do not want to pump up too much or become a bodybuilder, I don't think that will be an issue for you.
Hope I was of help there,friend. Just PM me if you want any other info or visit the site I mentioned above. Cheers!