If you apply this idea to the structure of an atom, in the older, Bohr model, there is a nucleus and there are rings (levels) of energy around the nucleus. The length of each orbit was related to a wavelength. No two electrons can have all the same wave characteristics. Scientists now say that electrons behave like waves, and fill areas of the atom like sound waves might fill a room. The electrons, then, exist in something scientists call "electron clouds". The size of the shells now relates to the size of the cloud. This is where the spdf stuff comes in, as these describe the shape of the clouds.

Look at the Heisenberg uncertainty principle in a more general way using the observer effect. While Heisenberg looks at measurements, you can see parallels in larger observations. You can not observe something naturally without affecting it in some way. The light and photons used to watch an electron would move the electron. When you go out in a field in Africa and the animals see you, they will act differently. If you are a psychiatrist asking a patient some questions, you are affecting him, so the answers may be changed by the way the questions are worded. Field scientists work very hard to try and observe while interfering as little as possible.

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Physics4Kids.com: Modern Physics: Quantum Mechanics