Bodybuilding is a sport that has been around for generations and it is something that most people assume is very hard to do
. It's actually quite simple. I don't want to simplify what many bodybuilders do over the course of years as "simple", but the process isn't exactly that hard. The hard part is applying the simplicity day after day with little to no rewards. When you get right down to it bodybuilding is a sport of patience and being as consistent as possible. A person that seeks instant gratification is often the first person to give up because bodybuilding takes time.
As for how you learn bodybuilding, it is just a matter of working out hard and eating properly. I've found the way to eat properly is to go on bodybuilding forums and talk with people. The fact is that your diet is far more complicated than anything you'll do in the gym. I'd love to give you a step by step plan, but your diet needs to be unique for you. There are some people that need to eat a ton of food or they'll never gain of a pound of muscle and other people have to watch what they eat or they'll put on fat.
As for what you should be doing in the gym, I've found the best way is to watch what other people are doing. I like to watch videos to see if I'm doing it right. Remember to always watch yourself in the mirrors to make sure you're using correct form. Start with light weights to begin, just to make sure you're doing the form properly.