## Assign the numbers 1-10 to array @arr
@arr = 1..10;

## Pass @arr by reference to function randomize()
randomize(\@arr);

## When used in this context, the array prints
## with space delimiters between items
print "@arr";

sub randomize {
    ## Declare variables inside the scope of
    ## this function
    my ($p, $size, $swap, $key);

    ## Assign the array reference passed to
    ## the function to $p
    $p = $_[0];

    ## Assign the length of the array pointed
    ## to by $p to $size. This is the number
    ## of items in the array - 1
    $size = $#$p;

    ## Randomize all items up to the next to
    ## last item. The last item is randomized
    ## already if the other items are.
    for (0..($size-1)) {

        ## Pick a random item from current
        ## position to end
        $swap = int rand($size - $_ + 1) + $_;

        ## Swap item with current position
        $key = $p->[$_];
        $p->[$_] = $p->[$swap];
        $p->[$swap] = $key;
    }
}
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You should probably look up $_ and @_ and read up on references, it will help you understand this a bit.