This is your first problem to why you are skinny you need a gym

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Samson said it best go to a gym get a trainer to work with you and set up a program of some sorts with a lot of compound movements like deadlifts /bench /squats /clean and press.If you are a total beginner some movements are going too advanced but a good trainer will help you.
Second... you can lift until the cows come home but if you don't eat to gain weight you will look like Leonard Deskinnio.
Nutrition is 75% of how you look and you can eat to lean out and drop fat and you eat certain ways to bulk up find out this info before you step foot in a gym.
Thirdly...Why would you want to have a body like Brad Pitts????

He is skinny except in Troy so if you want a Brad Pitt body lol go for the Troy look if you must.I would go more Edward Norton American History X llook if I was you more than Brad Pitt but whatever floats your boat.Nutrition + gym = a start.
Push ups and sit ups at home + salad and fruit=Brad Pitt(except Troy)
good luck to you its not easy.