Noob style and code suggestions posted here, with your code, formatted:

#! /usr/bin/perl
#
#
#

use strict;       # --- Good job on using strict and warnings !!
use warnings;

#------------------data-------------------------
my @Rainfall ;    
my $Index ;       # --- Perl programmers try to avoid using Indexes wh
+ere not necessary.
                  # --- IN This case, Index is NOT necessary
my ($Total, $Average) = 0, 0; # Wrong intent (result would be OK) - er
+ror pointed out by others
#------------------program----------------------

print " Enter 12 numbers for the rainfall for each month \n";

for ( $Index = 0; $Index < 12 ; $Index++ )  # --- Perl programmers wou
+ld not use "C" style loop
{
 print "Enter a month's rainfall: " ;
 chomp($Rainfall[$Index]= <STDIN>);    # ---
}
 
  # --- Perl programmer would have done this like:
  # --- while (<STDIN>){
  # ---    chomp;
  # ---     push @Rainfall, $_;
  # ---  } 

#
# now we have all the input, we can do things with it:
#

foreach (@Rainfall)       

{

$Total = $_; 

  # --- Perl programmer would have done:
  # --- foreach (@Rainfall) {
  # ---    $Total += $_;
  # --- }
  # --- print "Total=$Total;  Average = " , $Total/scalar(@Rainfall) ,
+ "\n"; # Should have formatting for Avg...
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