First of all
www.bodybuilding.com is your friend. Tons of good articles. I was am in pretty much the same boat as you. I am an ectomorph and I have a fast metabolism, which makes it hard for me to put on weight. I have started working out about 3 months ago, and I have already seen awesome results. I would suggest first and foremost to start eating. Healthy and high protein foods. Get a membership to the gym and start a program. The one im currently doing is a 5 day split workout.
Day 1-Chest and Biceps
Day 2-Cardio and Abs
Day3-Legs
Day4-Triceps and Back
Day5-Rest
Day6-Shoulders, Cadio and abs
Day7-Rest
For each body part I do three excersizes a day. So in total generally 6 excersizes a day.
I would suggest drinking whey protein shakes in the morning and after you workout. And maybe even thinking about taking creatine. I will post more later. And I am by no means an expert, you can listen to me because this is what has worked for me. But other people who have been doing this longer may be able to help you more.