If you want to display their info at the bottom or beginning of the post, then use this and place it in the corresponding area of your WordPress files. (i.e. Single.PHP or Comments.PHP)

<div class="author-box">
   <div class="author-pic"><?php echo get_avatar( get_the_author_email(), '80' ); ?></div>
   <div class="author-name"><?php the_author_meta( "display_name" ); ?></div>
   <div class="author-bio"><?php the_author_meta( "user_description" ); ?></div>
</div>

Edit the author box as necessary.