1) Exporter is a way to export names into your namespace. If you use a module that doesn't use Exporter or something similar, you can still use the module, but for example a sub DoPiff() in module Bang cannot be called as DoPiff() (would generate an error) but only as Bang::DoPiff()

2) not really understanding the question.

3) If you don't use, require, do or eval a module, that module doesn't exist for your script.