This one's fairly simple, actually. There are really only two parts: An assignment to $_ and a back-tick running of $_.

If you break down the first statement, you'll see it's two strings XOR'd together:

$_ = '%#(/@*(((@!./((%)@+%),@(!#+%)@#/.' # The encrypted string
     ^ # XOR
     '@@@@``][\`@@@\@@[`{@[@`@@@@@[~@@@' # The secret decoder ring
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So this ends up assigning 'echo Just another Perl hacker>con' to $_. The second line, `$_` simply passes that to the shell and runs it, which will work fine on any Win32 system.