Can someone give me an example of a practical use for an array in a game?
Arrays are probably the single most powerful construct in any programming language, including C2. The following are just trivial examples.
A 1D (1 dimensional) array can store (and allow you to easily retrieve) a list of numbers or text.
A 2D array is like a grid and so is good at storing, e.g. a level full of things that you can easily access via x,y coordinates.
3D arrays are useful but less common IMO, you might use them to extend your 2D levels to have floors as well
They are powerful because you can go through them in a 'loop', rather than one by one. Or grab one randomly by its 'index'