WordPress : Filter vs Action vs Loop

You're close but there are a couple of things that need to cleared up.

Actions and Filters are Hooks, not loops.

Action hook adds something while WordPress is loading, you can see this when you enqueue your CSS or JavaScript files. Here is an example:

<?php 
function my_scripts_method() {
    wp_enqueue_script( 'scriptaculous' );
}
add_action( 'wp_enqueue_scripts', 'my_scripts_method' );

Filter hook is when you want to modify data of a function. here is an example:

<?php
function wporg_filter_title($title)
{
    return 'The ' . $title . ' was filtered';
}
add_filter('the_title', 'wporg_filter_title');

The difference between the two by looking at the examples are Actions are adding to WordPress core, and filter is modifying a WordPress function.

Loops are just that a loop, nothing more. Just like in JavaScript using the while loop in PHP/WordPress is the same. we create a condition and check that condition and if true or not, or while something is true or not we tell it to do something.

Here is a common loop in WordPress:

<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

        <h2><?php the_title(); ?></h2>
    <?php the_post_thumbnail(); ?>
    <?php the_excerpt(); ?>
<?php endwhile; else: ?>
    <?php _e( 'Sorry, no posts matched your criteria.', 'textdomain' ); ?>
<?php endif; ?>

Here is The Loop in action. We are saying, if there are posts, and while there are posts get the post and do this. We state where we end the loop with the endwhile statement then end the if statement after.

Hooks do not loop they are modifiers or hooks that you "hook" into WordPress while loading. A loop is just that looping through some conditional statement and performing a process that you state.