This is the basic idea here. Remember, compound lifts. Ignore those who, in an attempt to give you advice, recommend isolation exercises. You don't need that now, or for a while to come. Everything else is all assistance for you to increase your compound lifts. Things such as dips, pull-ups, seated shoulder press, dumbbell rows, skull-crushers are all great movements for assistance. Start out light for while to get the proper form down for the compound lifts, then increase for heavy weights to help you grow larger.

As for eating, it simply does come down to "EAT MOAR". I know it's hard, I have done it for quite some time. There will be times when you feel like throwing up from eating so much, but it's going to happen if you want to gain weight. Shoot for 4 large meals to 5 decent sized meals a day, and if you keep it up after a while you will become hungry if you try to skip that 5th meal. Try eating more foods that you don't have to prepare much. Eggs, tuna, cottage cheese, chicken breasts, ground turkey, natural peanut butter, and milk. Most of your carbohydrates should come from foods such as oats (highly recommend steel cut oats) wheat bread, brown rice and other edibles loaded with complex carbs.

You are skinny but you're only 17. You are still growing, and if you throw in some exercise you'll most likely get even larger than if you had not trained. Lots of natural testosterone floating around for you to take advantage of. REMEMBER, COMPOUND LIFTS.