show specific posts by category code example
Example: show all posts from category
<?php
$args = array( 'category' => 7, 'post_type' => 'post' );
$postslist = get_posts( $args );
foreach ($postslist as $post) : setup_postdata($post);
?>
<h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
<?php the_excerpt(); ?>
<?php endforeach; ?>