Add the following lines to your current activated WordPress Theme’s template file, preferably your Theme’s template functions.php file:

add_filter( 'allow_subdirectory_install',
	create_function( '', 'return true;' )
	);

You can remove the lines above once you done enabling the Network feature.

Creating this into a plugin is not an option, since all plugins are required to be deactivated before enabling the Network feature. Please read on how to Create A Network in the WordPress Codex and ticket #12931 for more information on why it is block by default.

Add the following Conditional Tags test snippet to your WordPress Theme’s template file, preferably your Theme’s template sidebar.php file:

<?php
$conditions = array(
  'is_home()',
  'is_front_page()',
  '$wp_query->is_posts_page',
  'is_page()',
  'is_single()',
  'is_singular()',
  'is_attachment()',
  'is_search()',
  'is_archive()',
  'is_category()',
  'is_tag()',
  'is_tax()',
  'is_author()',
  'is_day()',
  'is_month()',
  'is_year()',
  'is_time()',
  'is_date()',
  'is_paged()',
  'is_comments_popup()',
  'is_preview()',
  'is_404()',
);

echo '<h2>Conditional Tag</h2><ul>';
  $i = 0;
  foreach ( $conditions as $condition ) :
    $condition = str_replace('()', '', $conditions[$i]);

    switch ( $condition ) :
      case 'is_front_page' :
        $query = is_front_page();
        break;
      case '$wp_query->is_posts_page' :
        $query = $wp_query->is_posts_page;
        break;
      default :
        $query = $wp_query->$condition;
        break;
    endswitch;

    echo '<li><code>' . $conditions[$i] . '</code>';
    echo $query ? ': <span style="color:green">true</span>' : ': <span style="color:red">false</span>';
    echo '</li>';

    $i++;
   endforeach;
echo '</ul>';
?>

Note: Currently, there’s no is_posts_page() conditional tag yet.

This is how you can display the content of the Page along with the latest Posts.

Add the following lines to your WordPress Theme’s template index.php file, preferably before the loop:

<?php
if ( 'page' == get_option('show_on_front') && get_option('page_for_posts') && is_home() ) : the_post();
	$page_for_posts_id = get_option('page_for_posts');
	setup_postdata(get_page($page_for_posts_id));
?>
	<div id="post-<?php the_ID(); ?>" class="page">
		<div class="entry-content">
			<?php the_content(); ?>
			<?php edit_post_link('Edit', '', '', $page_for_posts_id); ?>
		</div>
	</div>
<?php
	rewind_posts();
endif;
?>

• function limit_posts_per_page() {
  	if ( is_category() )
  		return 2;
  	else
  		return 5; // default: 5 posts per page
  }
  
  add_filter('pre_option_posts_per_page', 'limit_posts_per_page');
  

• function limit_posts_per_archive_page() {
  	if ( is_category() )
  		set_query_var('posts_per_archive_page', 2); // or use variable key: posts_per_page
  }
  
  add_filter('pre_get_posts', 'limit_posts_per_archive_page');
  

The code example above is for showing 2 posts per page when any Category archive page is being displayed. Same results in two different way.

For more possible page conditions, please refer to the Conditional Tags page in the WordPress Codex.

function gallery_columns($content){
	$columns = 2;
	$pattern = array(
		'#(\[gallery(.*?)columns="([0-9])"(.*?)\])#ie',
		'#(\[gallery\])#ie',
		'#(\[gallery(.*?)\])#ie'
	);
	$replace = 'stripslashes(strstr("\1", "columns=\"$columns\"") ? "\1" : "[gallery \2 \4 columns=\"$columns\"]")';

	return preg_replace($pattern, $replace, $content);
}

add_filter('the_content', 'gallery_columns');

$columns can be set to any numeric value. If [gallery] columns is set to 0, no row breaks will be included.

Plugin download: Gallery Columns

add_filter('gallery_style',
	create_function(
		'$css',
		'return preg_replace("#<style type=\'text/css\'>(.*?)</style>#s", "", $css);'
		)
	);

To display in single post view, add the following line to your WordPress Theme’s template single.php file within The Loop:

<p>Shortlink for this post: <?php echo get_shortlink(get_the_ID()); ?></p>

Add the following lines to your WordPress Theme’s template functions.php file (For example, functions.php file for a Theme named “default” would probably reside in the directory wp-content/themes/default/functions.php) or create it as a Plugin by filling the additional Standard Plugin Information:

add_filter('author_link', 'author_url');
	function author_url($url) {
		if (get_the_author_meta('user_url'))
			$url = get_the_author_meta('user_url');		

		return $url;
	}

Add within The Loop:

<span class="author vcard">
	by <a class="url fn n" href="<?php echo get_author_posts_url(get_the_author_meta('ID')); ?>"><?php the_author(); ?></a>
</span>

The example below will overwrite the default and only allows <a> tag with href and title attribute; <strong>, <em>, <code>, <ul>, <ol> and <li> tags to be used in comment (paragraph and line breaks automatically).

Add the following lines to your WordPress Theme’s template functions.php file (For example, functions.php file for a Theme named “default” would probably reside in the directory wp-content/themes/default/functions.php) or create it as a Plugin by filling the additional Standard Plugin Information:

<?php
 $allowedtags = array(
   'a' => array ('href' => array (), 'title' => array ()),
   'strong' => array(),
   'em' => array(),
   'code' => array(),
   'ul' => array(),
   'ol' => array(),
   'li' => array()
 );
?>

To display all of the current allowed tags for comment within the comment area, edit your WordPress Theme’s template comments.php and add allowed_tags() template tag.

For example:

<p>You can use these tags: <code><?php echo allowed_tags(); ?></code></p>

Example

The [gallery] shortcode is used in a Post or Page to display a thumbnail gallery of images attached to that post. It can be used in its simplest form.

Source: http://codex.wordpress.org/Gallery_Shortcode