One of the most important lessons for those new to beer brewing is proper cleaning and sanitation. All around us there are invisible bacteria, germs, and wild yeast that like your beer as much as you do. These microorganisms are unwelcome guests to the party, however, because if they get into your beer, they can contaminate it and infect it.
It is the home brewers job to provide the yeast a healthy environment during fermentation, and to give the yeast a head start before these other organisms can take hold. Certain precautions must be taken during the beer brewing process to prevent contamination. That is why it is critically important that you are thorough in cleaning and sanitizing your beer brewing equipment.
It is important to note that cleaning and sanitation DO NOT mean the same thing. Sanitation goes beyond simple cleaning. Chemical sanitizers must be used in the beer brewing process to eliminate the majority of the microorganisms on the equipment beyond what simple soap and water can accomplish alone.