I'm not sure I understand correctly what you want to do, but I'll try:

my $sentence = 'Sam goes to school to play football.';

substr($sentence, $_, 0) = '**' for 35, 27, 18, 12;

print $sentence, "\n";
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This will print Sam goes to **school** to play **football**., and the asterisks have been put there using the character offsets.

However, a more straightforward way to highlight school this way would be something like:

$sentence =~ s/(school)/**\1**/;
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Update: Sorry, I forgot the part about the word count.. Well, here's a way to get to the "4" (not very nice, maybe others have a more beautiful solution):

my $sentence = 'Sam goes to school to play football.';

# Count the spaces and add 1
my $count1 = substr($sentence, 0, 12) =~ y/ // + 1;
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