How to add a byline to all the pages?

You will do this in your theme and HOW you do it will depend on how your theme is set up. But to give a quick example, I’ll show you how to do it with any template with a loop.

<?php 
    if ( have_posts() ) {
        while ( have_posts() ) {
            the_post(); 
               echo ('<p>This post was written by'. get_the_author().'</p>'); // I ADDED THIS LINE ONLY TO THE LOOP
            //
            // Post Content here
            //
        } // end while
    } // end if
?>

from the Codex:

Displays the value in the user’s Display name publicly as field.

So just set all your authors to the full name (as per Google Authors requirements) and then add the author tag into each page template you want to show the author on. Common ones are post.php, page.php, index.php Newer themes may have a page-content.php or even I’ve seen the_loop.php so where you put the tag will depend on your theme’s structure.

You can also use the_author if you are using the tag outside of the “echo”