By default it works on STDOUT. (As has been said, select() another filehandle to change the autoflushing on it.) Note that unlike your example, you should use it prior to performing any operations on that filehandle:

$|++;
print "asd";
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As, again, has been said, the variable is really called $|, and the long name is only available if you use English;. You can also use IO::Handle; and then say STDOUT->autoflush(1);.

Makeshifts last the longest.