What you show is typical for class methods, though $_[0] would ordinarily be called $class or $stash when it's shifted in.

Usually the leading underscore signifies an internal function which should not be called from other namespaces. That is a convention, Perl does nothing to enforce it.

If you want an ordinary function, not a class method, leave out the class name shift and call like this:

$foo = Whaterverlib::pmfile::nameoffunction($sent);
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with nameoffunction written as,

sub nameoffucntion {
    my $recieved = shift;

    my $value = whatever;
 
    return $value;
}
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In general, dereference arrow notation puts an extra argument in @_ - either the name of the class, or a reference to the instance which called the object method.