Most variables that you deal with contain one value. Sometimes however it's useful to store more than one value. Arrays are one way to do this. Since I can't come up with a good simple definition I'll turn to Microsoft's definition from the VBScript documentation:

Array

A set of sequentially indexed elements having the same type of data. Each element of an array has a unique identifying index number. Changes made to one element of an array do not affect the other elements.

For the rest of the details check out the code. It's easier to show you this stuff than to try and explain it without an example to refer to.