I need to be able to show some informations only to the author in his profile viewable in the front end, for istance I need to add a text under the avatar that only the author, if logged in, can see. This text will inform them that they can change the avatar anytime by adding it in their profile page... I could also add some more details... Is there a way to achieve this? Thanks!
You can check who the current user is and whether they have the same ID as the user that is being viewed.
global $current_user wp_get_current_user(); if(the_author_meta('ID') === $current_user->ID) : // Add your code here... endif;
See these Codex pages for more information -