excerpt in template for specific page

The following code will query the “blog” category for the latest three published posts and loop through these results to display the excerpt from each.

$args = array(
    'category_name' => 'blog',
    'post_status' => 'publish',
    'posts_per_page' => 3,
);

$blog_posts = new WP_Query( $args );

if ( $blog_posts->have_posts() ):
    while ( $blog_posts->have_posts() ): 
        $blog_posts->the_post();

        // Do stuff with each post
        echo get_the_excerpt() . "<br>";

    endwhile;
    wp_reset_postdata();
endif;

WordPress Codex is a great resource for WP development. The WP_Query class is incredibly powerful and well-documented here: https://codex.wordpress.org/Class_Reference/WP_Query#Category_Parameters