What are unit cells, and how do you determine the number of atoms in one of them?

I've read several websites to try to figure out what exactly a unit cell is, but I can't seem to understand it. Could someone explain what a unit cell is, and the different types? Thanks!




The [unit cell](https://en.wikipedia.org/wiki/Crystal_structure#Unit_cell) is the most primitive 3D structure that contains the arrangement of atoms which form the crystal of a compound. The unit cell is probably most meaningful in the study of minerals, so it is more of an inorganic analytical technique rather than an organic analytical technique. There are 7 3D [crystal lattice systems](https://en.wikipedia.org/wiki/Crystal_structure#Lattice_systems) which form 14 primitive 3D forms called the [Bravais lattices](https://en.wikipedia.org/wiki/Bravais_lattice). The 14 Bravais lattices can be further subdivided into [32 point groups](https://en.wikipedia.org/wiki/Crystal_system#Crystal_classes). 


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