<?php
function my_load_scripts($hook) {
    wp_enqueue_script( 'custom_js', plugins_url( 'js/custom.js', __FILE__ ), array(), '1.0.0' );
    wp_register_style( 'my_css',    plugins_url( 'style.css',    __FILE__ ), false,   '1.0.0' );
    wp_enqueue_style ( 'my_css' );
 
}
add_action('wp_enqueue_scripts', 'my_load_scripts');

<?php
add_image_size('custom-size', 220, 180, true ); 

<?php
function example_callback( $example ) {
    // Maybe modify $example in some way.
    return $example;
}
add_filter( 'example_filter', 'example_callback' );

<?php
get_header();
 
if ( have_posts() ) : 
    while ( have_posts() ) : the_post();
        the_content();
    endwhile;
else :
    _e( 'Sorry, no posts matched your criteria.', 'textdomain' );
endif;
 
get_sidebar();
get_footer();