There are actually two questions here: "Why is my code doing that" and "How do I do what I want". First the "Why".

You read a line at a time, so far so good. Then, for each line, you split the line on whitespace to generate a list of words (in @line?). Then you print the second word in the list - that is, you print the second word from each line - with no whitespace.

What you want to do is find each word with a p in it. "Find each" should generally fire the grep neuron in your brain. Consider:

#!usr/bin/env perl

use warnings;
use strict;

while (<DATA>) {
    my @words = split ();
    my @pWords = grep {/p/i} @words;

    print "Line $. contains ";
    if (@pWords) {
        print "the following words containing p: @pWords\n";
    } else {
        print "no words containing p\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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Prints:

Line 1 contains the following words containing p: CPAN comprehensive P
+erl
Line 2 contains the following words containing p: expression.
Line 3 contains the following words containing p: /pattern/ pattern op
+erator.
Line 4 contains the following words containing p: Perl
Line 5 contains the following words containing p: help.
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