__declspec( dllexport/dllimport )

Could you please explain to me the purpose of dllexport/dllimport. I've read that the dllexport statement makes the function/variable available to anyone using that .dll. (which seems to be untrue about variables.)
I know very little about .dll's so please give the explanation in simple terms.
Thank you.

>>3
What do you mean by "expose". Also why does the keyword only apply to functions, msdn examples show it being used with simple variables, but I'm still able to access them without dllexport.