The key is the y///. The code simplifies into this:

$_ = '=]=>%-{<-|}<&|`{';
y/ -\/:-@[-`{-}/`-{~" -/;
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The y operator is the same thing as the tr operator. The mapping looks like this:

 -/:-@[-`   --->    `-{~
      {-}   --->    " -
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That's the range of space through forward-slash, concatented with the range of colon through at-sign, and left-square-bracket through backquote, maps onto the range from ` to left-curly-bracket, plus the tilde character. If we check the ASCII character set, we can simplify this into:

 -/       --->    `-o
:-@       --->    p-v
[-`       --->    w-{~
 {        --->    "
 |        --->    space
 }        --->    -
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So now, we can rewrite this as:

$_ = '=]=>%-{<-|}<&|`{';
tr/!-\//a-o/;
 tr/:-@/p-v/;
 tr/[-^/w-z/;
 tr/`/~/;
 tr/{/"/;
 tr/|/ /;
 tr/}/-/;
print;
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It's just a sneaky way to map punctuation characters into alphabet letters.