People tend to make muscle building a lot harder than it should be.
I can't say I blame them.
With a plethora of muscle building magazines, stores full of hard to pronounce supplements, and advertisements promoting the latest fitness fad it's pretty easy to get overwhelmed quickly.
The truth is...
the basic concept of muscle building is actually pretty simple.
To gain muscle you must do two things:

1. Eat more calories than you expend
2. Break down muscle fibers through physical exertion in order to grow them back bigger (usually through weight-training)

These 2 critical principles are the foundation for any sound muscle building program.
Now...
here's where things can get tricky.
If you don't already know how to eat or weight-train properly then you must to learn how to do them CORRECTLY.
To tell you the truth, this is hard part.
It takes many hours of research and many, many grueling weeks and months of real live application to master nutrition and weight-training.
The reason that it is so hard is because nutrition and weight-training for muscle growth have many in-depth intricacies, rules and best practices.
So rather than try to teach you everything, I will provide you the essential framework for muscle building in a simplified fashion.
Eating Made Simple:

• Determine Your Daily Muscle Building Calorie Intake Level.
  There aremany advanced formulas to do this.
  A very basic one is to multiply yourbody weight by 20.
  (So if you weigh 140lbs eat around 2800 calories a day)

• Eat 5-6 Times a Day.
  Yes it's possible.
  Initially it will be hard, but your body will adapt if you are disciplinedenough to make yourself eat every 2-3 hrs.
  

• Eat Well-Balanced Meals.
  Feedyourself the right way.
  Just because you are eating more calories does notallow you to eat unhealthy.
  NO JUNK FOOD.
  You should eat balanced portionsof complex carbohydrates, proteins, and essential fats.
  

• Consume Plenty Of Protein.
  Proteinis an essential ingredient for muscle building.
  An old rule of thumb is toconsume at least 1g of protein per lb of bodyweight a day (If you weigh140lbs consume 140g of protein).
  

• Drink A Lot Of Water.
  It cannot be overemphasized how important water is.
  For a very basic calculationdrink a minimum of ½ your bodyweight in ounces.
  (If you are 140lbs drink at least 70 ounces a day)

Training Made Simple:

• Develop A Weight-Training Routine.
  Weight-TrainingRoutines are widely available through books in print and on the internet.
  A weight-training routine will outline which exercises need to be performed,when they should be performed and how many times they should be performed.
  

Any sound muscle-building weight-training routine will require you to...

• Weight-Train INTENSELY.
  Place yourmuscles under stress far above and beyond normal circumstance to promotegrowth.
  This means train with maximumeffort every repetition of every exercise.
  

• Lift Heavy Weights.
  Lift HEAVYweights to achieve maximum muscle fiber break down.
  

• Progressively Increase.
  Systematically increase the difficulty of your workouts to continuallychallenge your muscles.
  This means increase weight or repetitionsperformed (or both) for each workout.
  

• Allow Adequate Time To Rest.
  Muscles need time to FULLY RECOVER after being subjected to intensestress.
  Do not work out a single muscle group directly more than twice aweek.
  (Working a muscle group directly only once a week is often the recommendedstandard)

• Limit The Length Of Your Workouts To60 Minutes Or Less.
  Prolonged intense physical exertion beyond onehour can lead to increased muscle loss.
  

• Workout No More Than 3-4 Days as a Beginner.
  Over-training is a fundamental errorof many beginners.
  To reiterate your body needs time to FULLY RECOVER fromprevious weight training sessions.
  

• Workout All Of Your Muscles.
  Incorporateweight lifting exercises to stimulate muscle growth throughout your ENTIRE body for maximum overallmuscle growth and to keep muscular symmetry.
  

• Be Safe - Exercises performed withfree weights can be very dangerous if not performed properly.
  If you areinexperienced it is highly recommended to do adequate research on thematter to perform the exercises safely and correctly.
  

Where To Go From Here: Remember what I have provided is just the essential framework for building muscle in a basic simplified format.
If you follow the key points here you WILL gain muscle, however, you still should continue researching to gain a FULL understanding of the principles I have laid out.
There are many great guides on the internet that will give you an in-depth, comprehensive review of the basic information I have provided you.
Just remember everything you learn about muscle building going forward should relate back (in some fashion) to the two the simple overarching principles outlined here (Nutrition & Training).
Good luck on your muscle building journey!