Can’t understand apply_filter logic

by

Thanks for your answers. According to comments above, I modified my code. Now it works. Is it correct way?

<?php
/*
Plugin Name: Test plugin
*/

$arr = [];

add_action( 'init', 'set_var_data' );

function set_var_data() {
    global $arr;

    $arr = [
        'val',
        'val2',
        'val3'
    ];

    $arr = apply_filters( 'my_hook', $arr );
}

print_r( $arr );