Where did you put your expe.pm module? It has to be in c:/Perl/bin/ if you want this to work, and the error message shows that this is not the case.
For your other questions:
This is defining the @EXPORT_OK array as an array contain ing just one element, const.
This is saying that you want to use the expe module and that, in this module, you want to use "const".
Two differents things.