How to show all posts of the category in wordpress?

   <?php
    $args = array( 'category' => 7, 'post_type' =>  'post' ); 
    $postslist = get_posts( $args );    
    foreach ($postslist as $post) :  setup_postdata($post); 
    ?>  
    <h2><a href="https://wordpress.stackexchange.com/questions/17496/<?php the_permalink(); ?>"><?php the_title(); ?></a></h2> 
    <?php the_excerpt(); ?>  
    <?php endforeach; ?> 

just change the category id (number 7)
and change the post_type that was in the plugin

to learn more about post_type, see link
http://codex.wordpress.org/Custom_Post_Types