Since you have a slender build, you're going to want to eat a lot. But don't go eating all the junk in your cabinets...you need to eat a lot of good/healthy food. You want to make sure that you take in a lot of calories. You need to make sure that the number of calories that you intake is greater than the number of calories that you burn during your workouts; that's how you grow. Simple, but no.

With a healthy diet and exercise routine, you should be good to go.

DO NOT expect immediate results. Body transformation is something that may take many months...even years. Patience is the key to many things in life...bodybuilding happens to be one of them.

Good luck.