Get featured image WordPress

How to show featured image from wordpress post or page?

On this page

Examples

<?php if (has_post_thumbnail($post->ID)): ?>
    <?php $image = wp_get_attachment_image_src(
        get_post_thumbnail_id($post->ID),
        "single-post-thumbnail"
    ); ?>
    <div id="custom-bg" style="background-image: url('<?php echo $image[0]; ?>')"></div>
<?php endif; ?>