Members are read/write(most) variables pertaining to the object.
Used by creating a new object and referencing the member in pointer notation.
Such as:
my $map = new mapscript::mapObj("my.map");
$map->{name} = "NEWNAME";

Methods are functions pertaining to the object.
Used by creating a new object and referencing the method in pointer notation.
Such as:
my $map = new mapscript::mapObj("my.map");
my $layer = $map->getLayerByName("my_layer");