#!/usr/bin/perl -w

# always use strict and warnings (-w from above)
use strict;

# 1 and 2
my %new_hash = create_hash('in_file.txt');

# 3
while(my($key,$val) = each %new_hash) {
   print "$key => $val\n";
}

sub create_hash {
   my $filename = shift;
   my %hash;

   # 1.1
   open(FILE,'<',$filename) or die "can't read $filename: $!";

   # 1.2 - you get the point ;)
   while (my $line = <FILE>) {
      chomp $line;
      my($key,$val) = split (':',$line,2);
      $hash{$key} = $val;
   }

   return %hash;
}