How to show single post page as home page

It depends on what theme you use as they are not coded the same.

Use pre_get_posts or the reading settings and the_content() rather than the_excerpt() in your loop.

function wpsites_home_page_limit( $query ) {
    if ( $query->is_home() && $query->is_main_query() && !is_admin() ) {
        $query->set( 'posts_per_page', '1' );
    }
}
add_action( 'pre_get_posts', 'wpsites_home_page_limit' );

Or you could redirect the latest single post to display on the home page.