Hemsworth grew up playing sports, but he apparently never really lifted weights before the Thor movie. He started training to put on 20 lb on his 6'3" frame. He hit the weights hard and got serious about his eating plan. The results were apparent on the screen--he had a truly impressive physique.
Remember: the key to building muscles is the right kind of training and diet, not supplements.
I'd recommend a program like Jason Ferruggia's Muscle Gaining Secrets if you are new to training and want to put on muscle as quickly as possible.
More advanced trainees may want to check out MI40 Mass Intentions for building muscle.