You need to eat enough so that your muscles have the nutrients to grow. When you work out, your body uses carbs as energy (bread, pasta, etc.). After you're done working out, your body heals and rebuilds your muscles with protein (meat, cheese, etc.). And you need to make sure you're getting enough fat, but make sure it's the good kind (think olive oil, not that white sticky fat you pull off the side of a steak).
Everyone has a different body and a different metabolism. There isn't any diet that fits everyone. I or anyone here I'm sure can help you make a diet if you'd like too.
Exercises... I'm not sure about, I'm still learning that part myself. That's definitely something others can help you with.
Some supplements work, some are crap. The only supplement I truly trust is whey protein. If you're a skinny guy that's having trouble gaining weight, you should go for a weight gain whey powder.
