Add Custom Columns in the All Posts Table

functions.php

function add_acf_columns ( $columns ) {
	return array_merge ( $columns, array (
			'guide_level' => __ ( 'Guide Level' ),
			'guide_position'   => __ ( 'Guide Position' )
	) );
}
add_filter ( 'manage_guide_posts_columns', 'add_acf_columns' );

function guide_custom_column ( $column, $post_id ) {
	switch ( $column ) {
		case 'guide_level':
			echo get_post_meta ( $post_id, 'guide_level', true );
			break;
		case 'guide_position':
			echo get_post_meta ( $post_id, 'guide_position', true );
			break;
	}
}
add_action ( 'manage_guide_posts_custom_column', 'guide_custom_column', 10, 2 );