How to add an image caption / alt text or description with php?

Hi, I’m trying to add captions, alt text and description on images (actually a slideshow). I can add the image title with:

<h1><?php the_title(); ?></h1>

But how to do so for the captions, alt text and description fields?
Here’s a relevant sample of the rest of the code if it can help:

<div class="slide">

    <?php if ( get_post_meta( $post->ID, "slide_url_value", $single = true ) != "" ): ?>
    <a
    href="<?php echo get_post_meta( $post->ID, " slide_url_value ", $single = true ); ?>"
    title="<?php the_title(); ?>">
        <?php the_post_thumbnail( 'featured-slide', array( 'title' => get_the_title() ) ); ?>
    </a>

    <?php else: ?>
    <?php the_post_thumbnail( 'featured-slide', array( 'title'=>get_the_title() ) ); ?>
    <?php endif; ?>
        <h1><?php the_title(); ?></h1>

</div>

Maybe using <?php the_field(''); ?> with id slugs??
Thanks