"keys" will return the keys for a hash, and "values" will return all the values. For what you want to do, "keys" is the most useful - e.g.

use strict;
my %hash = ('a'=>'hello', 'b'=>'goodbye', 'c'=>'foobar');

foreach my $key(keys %hash){ # iterates over 'a', 'b' and 'c'
  print "the value of $key is $hash{$key}\n";
}
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One point to note is that the order of the returned keys is not predictable (I get c,a,b in the above example).