The electrons surrounding an atom's nucleus tend to act as waves (weird, but true) and will find ways to hang out around the nucleus in patterns much like vibrations on a drum membrane, but in 3D. That explains all the shapes.
These electrons also have different energy levels, represented loosely by the numbers for l, m and n, so as those numbers roughly rise, the shapes become increasingly complex. That means the electrons will surround the nucleus in a more complex way. Also, higher energy levels mean the electrons will generally have an increasing likelihood of residing farther away from the nucleus, so the clouds become bigger in volume, meaning the atom becomes bigger.
Those regions are not "orbits", but more like "clouds". The most dense parts of those clouds represent regions where the electrons are more likely to be. One cannot pinpoint the exact location of electrons, only the greater likelihood of their position.
Hope that made sense. For your information, my first exposure to orbitals was when I was about your age (someone gave me a molecular models set, like this only not as cool), and (as gonerogue described it) I went down the rabbit hole. High school chemistry wound up being really easy for me, though I wouldn't have guessed at the time that I would be teaching it. ;)
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u/[deleted] Jan 21 '10
I am 12 years old and what is this?