Hey Kiddy!
You can read about de Broglie wavelength in wikipedia. And the double slit experiment..also called Young's experiment..both are in Wikipedia and explain how a 'particle' is also a wave. A 'particle' is a quanta [a local lump] of a wave..a local concentration of an extended wave.
It is more modern to view an electron as a wavelike entity sort of like a 'cloud' around a nucleus..
What does this look like?
good illustrations here:
http://en.wikipedia.org/wiki/Atomic_orbital
An electron in the presence of a nucleus is constrained...to certain energy levels, for example...now called orbitals [not planet like orbits of the old classic deswcription].
Think of a violin string as an analogy: the ends are constrained,fastened, so it can have only certain tones...certain vibrational patterns and associated energies. It's energy levels are constained to certain values...it's degrees of freedom are limited. like a bound electron.
Think of the electron as a wave: When it's in free space the wave is everywhere, it extends all over the place. But when attracted by protons in a nucleus, for example, that wave is now localized...it's constrained and so its different from the free space case. And the constraint is also modified by the presence of other electrons and additional protons. Since the energy is contained in the wave, changing it's configuration via the presence of nearby particles changes the wave characteristic and most likely energy levels where the electron will be found. It's very unlikely for the electron to be found between allowed energy levels...that is unlikely to be found between designated orbital energy levels.
In contrast, a free electron can take on any energy level. But when it is part of an atom or a larger structure, it's constrained...it's degrees of freedom are determined and limited by the whole structure. So an electron's energy levels and degrees of freedom are determined by the numbers of protons in the nucleus as as well as the particular structure of a lattice, as examples. The Schrödinger wave equation describes these.
Another way to say this: This SIZE of an electron is determined by it's environment...in fact in some lattice configurations its observed momentum and mass also seems to change! Such fundamental particles may be 'elemenatry' but they are not simple!