Here's a good
read to get started.
Firstly, they can only be used for booleans. In a single 32-bit cell you have 32 booleans. You can easily stretch it beyond that using an array and some shifting trickery. Read through the tut I posted, it covers most of what you'll need to know.
Edit: Let me re-phrase, you have 32 booleans to work with in a single cell. You can also store other values but you're limited to the number of bits needed to represent the value.
ie.
32 numbers ranging from 0-1
16 numbers ranging from 0-3
8 numbers ranging from 0-15
4 numbers ranging from 0-255
2 numbers ranging from 0-65535
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