Let's look at the squat. It is a compound exercise. It
works the quadriceps, hamstrings, gluteus, lower back,
abdominals, hips, and abductors. Squats allow for
heavy weights to be lifted. This makes the squat an
incredibly effective muscle building exercise. Compared
to an isolation exercise such as the leg extension, which
only focuses on the quadriceps. From this simple example
you can clearly see how much more productive compound
exercises are for building muscle.
Free Weights VS. Machines
Free weight exercises are more effective for building
muscle then machine exercises. Machines make the exercises
easier to perform. You do not have to balance the weight
with machine exercises because the machine balances the
weight for you. You will get less muscle stimulation from
machine exercises because they do not require the same
concentration or effort as free weight exercises. Free
weights have a greater ability to involve stabilizer
muscles than machines. Free weights put you in a natural,
3 dimensional environment for exercise.
The majority of your exercises should be compound free weight exercises. This does not mean that you should avoid machine exercises or isolation exercises. They are easy to learn and there is a low risk of injury, which is great for people who are just starting out or for rehabilitation purposes. And there are some good machine exercises that cannot be duplicated with free weights such as various cable pulley exercises. However, the majority of lifters should always base their workouts around compound, free weight exercises and supplement their workouts with machine and isolation exercises.
I've put together a listing of the top 5 weight training
exercises for each bodypart. Complete with exercise
pictures and text descriptions that explain how to perform
all the movements with proper technique.