Difference between $::variable and $variable

I want to know the difference between,

1 . Declarations : $::varible and $varible

2 . Calling of functions :
$::functions_output .= ::flatten_list($item[1]); and
$function_output = flatten_list($item[1]);

re: Difference between $::variable and $variable

The "::" is used to differentiate namespaces. In the absense of a package name before ::, it points to 'main', which is the perl program you initiated by name. I can see no reason to use that syntax. As far as I know, there is no difference between these two lines:

$::functions_output .= ::flatten_list($item[1]);
$function_output = flatten_list($item[1]);

Some test code:

the above code will not work if the "strict" pragma is used, making it particularly useless as far as current standards of perl programing are concerned.