Well, here's what i would do, and presuming i can still read the output is tested and correct:

#!/usr/bin/perl -w
use strict;

while (<DATA>) {
    my @line = split (); 
        foreach my $word (@line) {
                if ($word =~ /P/i) {
                        print "$word\n";
                }   
        }   
}


__DATA__
CPAN stands for comprehensive Perl Archive Network.
^ and $ are used as anchors in a regular expression.
/pattern/ is a pattern match operator.
Perl is very easy to learn.
Enter 'H' or 'h' for help.
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Why?

Your use of split is fine. But you need to loop thru your array:

line 6: if it doesn't make sense, figure it out

line 7: ditto

line 8: ditto

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