I've marked the important part below. Basically, each key => value pair is passed to @arr as two items, then %hash is redefined as the first 10 items (5 key => value pairs) of @arr.

use strict;

my %hash;
while (<DATA>) {
    chomp; split(/ => /);
    $hash{$_[0]} = $_[1];
}
######
my @arr = (%hash); %hash = splice(@arr,0,10);
######
for (keys %hash) {
    print "$_ => $hash{$_}\n";
}

__DATA__
a => 1
b => 2
c => 3
d => 4
e => 5
f => 6
g => 7
[download]