Access current logged in user from loop

You mean when an user is logged in you want to display their post, and only their posts, to them?

If so, using query_posts() to initialize The Loop as shown below should get you started:

<?php
global $user_ID;
get_currentuserinfo();
if($user_ID) {
query_posts("author=$user_ID");
}
?>

EDIT: Stuck an if statement in for a bit of sanity.