Namaste’ Johny76,
The positive effects of incorporating Yoga into your life are as numerous and varied as the individuals who practice the ancient asanas. I agree that it does help having an instructor when possible (for a variety of reasons). I have been blessed with one on one yoga instruction - but I also have bought several DVD’s, VHS and watch the Oxygen channel when they aired Yoga with Steve Ross. My piont is, each way has merits and you will gain as much as you put into it!
The books begin to give an overview of what the poses look like, but for the beginner it may be difficult to attempt viewing your posture as if outside yourself. Whereas, an instructor can physically come to you and help you adjust your pose as your level of experience grows. A simple Down Dog has the potential to be much more difficult than it appears once you realize how many areas of the body are actually focused on at the same time.
Do not get discouraged. Do not expect immediate gratification. Yoga is something that has the potential to not only strenghten muscles, assist in toning, stimulating hormone production and/or internal organs–it also has subliminal processes that assist us with our mind / body connection.
Blessings & peace