The tongue is definitely one of the most amazing organs in the body. It enables you to taste, (yeah), helps us pulvarize food, and talk. It can even be used to express yourself by sticking it out at whomever you don't especially like.
The tongue has lots of germs attached to it. Most of bad breath comes from the tongue and not the stomach like a lot of people think. There are lots of nooks and crannies for food particles to stick in and ferment. This causes odors to come off of the tongue and your friends and family to take a step back.
You can also develop a yeast infection in the mouth, commonly known as thrush in infants, that will cause a cheesy white coating on the tongue and cause breath odor too.
So what do you do? Brush your tongue daily with a few vigorous strokes. If the coating on your tongue won't go away after a week you may need to see your doctor or dentist to see if it's something more serious.
Does your tongue look black and hairy? That is a condition known as--Black Hairy Tongue. Sometimes it's just really obvious. This can be caused by smoking or excessive peroxide rinsing. Rinsing with peroxide just really doesn't do much. It only kills bacteria that can't tolerate oxygen. The germs that can't handle oxygen are so deep in the spaces around the teeth, the peroxide probably will never reach them. So don't bother with it.
Once again, tongue brushing or even using a tongue scraper will usually take care of the problem. A note of warning--be careful with tongue scrapers. You can remove the top surface of the tongue and even cause bleeding. I know this from personal experience. Yes, sometimes dental hygienists can get a little carried away. My favorite scraper actually has a short bristled brush on the end and won't cause trauma.