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This is tutorial about how to adding Page Navigation in your WordPress theme without any plugin.

Open functions.php, and add code below.

/* Adding Page Navigation ********************************************/

	function pagenavi( $p = 2 ) { // pages will be show before and after current page
	  if ( is_singular() ) return; // don't show in single page
	  global $wp_query, $paged;
	  $max_page = $wp_query->max_num_pages;
	  if ( $max_page == 1 ) return; // don't show when only one page
	  if ( empty( $paged ) ) $paged = 1;
	  // echo '<span class="pages">Page: ' . $paged . ' of ' . $max_page . ' </span> '; // pages
	  if ( $paged > $p + 1 ) p_link( 1, 'First' );
	  if ( $paged > $p + 2 ) echo '... ';
	  for( $i = $paged - $p; $i <= $paged + $p; $i++ ) { // Middle pages
	    if ( $i > 0 && $i <= $max_page ) $i == $paged ? print "<span class='page-numbers current'>{$i}</span> " : p_link( $i );
	  }
	  if ( $paged < $max_page - $p - 1 ) echo '... ';
	  if ( $paged < $max_page - $p ) p_link( $max_page, 'Last' );
	}
	function p_link( $i, $title = '' ) {
	  if ( $title == '' ) $title = "Page {$i}";
	  echo "<a class='page-numbers' href='", esc_html( get_pagenum_link( $i ) ), "' title='{$title}'>{$i}</a> ";
	}

And then add <?php pagenavi(); ?> anywhere after the loop. Example: (more…)

Add a code check to stop these from being changed:

//Check and Set the Default Thumbnail Sizes
if(get_option('thumbnail_size_w')!=160)update_option('thumbnail_size_w',160);
if(get_option('thumbnail_size_h')!=80)update_option('thumbnail_size_h',80);
if(get_option('medium_size_w')!=640)update_option('medium_size_w',640);
if(get_option('medium_size_h')!=320)update_option('medium_size_h',320);
if(get_option('large_size_w')!=1280)update_option('large_size_w',1280);
if(get_option('large_size_h')!=640)update_option('large_size_h',640);

Then they can be called with get_the_post_thumbnail:

$id=$post->ID;
get_the_post_thumbnail($id, 'thumbnail'); // Thumbnail
get_the_post_thumbnail($id, 'medium'); // Medium resolution
get_the_post_thumbnail($id, 'large'); // Large resolution
get_the_post_thumbnail($id, array(480,240) ); // Other resolutions

References:
WordPress.org Forums