# Declare it
sub this_is_a_subroutine {
  # Your arguments are in @_.
  # Normally you'd do something more useful here.
  print "I'm doing something!\n";
  return "This is a return value!\n";
}

# Call it
print this_is_a_subroutine();

# And here I'm going to terminate this program and
# show you what output it would produce.
__END__
I'm doing something!
This is a return value!