There are several ways,
1) Use other pages/posts and include them into the page.
<?php $recent = new WP_Query("page_id=**ID**"); while($recent->have_posts()) : $recent->the_post();?>
<h3><?php the_title(); ?></h3>
<?php the_content(); ?>
<?php endwhile; ?>
make sure you put the page ID you want to use, and it will pull that page into the page you are working on.
2) Many themes come with several widgets, but you can also build your own, and place it where you want to on a page.
there are more options, but this is a start.