WordPressc single page, archive page and 404 page

To enable comment: 

functions.php function comment_scripts(){
if ( is_singular() ) wp_enqueue_script( 'comment-reply' );
}
add_action( 'wp_enqueue_scripts', 'comment_scripts' ); 
To enable featured image: 

functions.php 

add_theme_support( 'post-thumbnails', array( 'post' ) ); 

To enable crop feature: 

functions.php

set_post_thumbnail_size( 200, 200, true );
add_image_size( 'post-image', 150, 150, true ); 

Using Featured Image:

functions.php

add_theme_support( 'post-thumbnails', array( 'post' ) ); 
<?php the_post_thumbnail('post-general-thumb', array('class' => 'img-responsive ')); ?>

single.php in WordPress:

<?php if(have_posts()) : ?><?php while(have_posts()) : the_post(); ?>
<?php the_title(); ?>
<?php the_content(); ?>
<?php comments_template( '', true ); ?>
<?php endwhile; ?>
<?php else : ?>
<?php _e('404 Error: Not Found'); ?>
<?php endif; ?> 

archive.php in WordPress:

for Archive & Archive Post List

  <h1>
<?php if (have_posts()) : ?>
<?php $post = $posts[0]; // Hack. Set $post so that the_date() works. ?>
<?php /* If this is a category archive */ if (is_category()) { ?>
<?php _e('Archive for the'); ?> '< ?php echo single_cat_title(); ?>' < ?php _e('Category'); ?>
<?php /* If this is a tag archive */ } elseif( is_tag() ) { ?>
<?php _e('Archive for the'); ?> < ?php single_tag_title(); ?> Tag
<?php /* If this is a daily archive */ } elseif (is_day()) { ?>
<?php _e('Archive for'); ?> < ?php the_time('F jS, Y'); ?>
<?php /* If this is a monthly archive */ } elseif (is_month()) { ?>
<?php _e('Archive for'); ?> < ?php the_time('F, Y'); ?>
<?php /* If this is a yearly archive */ } elseif (is_year()) { ?>
<?php _e('Archive for'); ?> < ?php the_time('Y'); ?>
<?php /* If this is a search */ } elseif (is_search()) { ?>
<?php _e('Search Results'); ?>
<?php /* If this is an author archive */ } elseif (is_author()) { ?>
<?php _e('Author Archive'); ?>
<?php /* If this is a paged archive */ } elseif (isset($_GET['paged']) && !empty($_GET['paged'])) { ?>
<?php _e('Blog Archives'); ?>
<?php } ?>

For archive post query: <?php get_template_part( 'post-excerpt' ); // Post Excerpt (post-excerpt.php) ?>  

If no post in archive or 404:

<?php else : ?> <h3>< ?php _e('404 Error: Not Found'); ?>
<?php endif; ?>  

404.php in WordPress:

<h2>404 Error: Not Found
<p>Sorry, but the page you are trying to reach is unavailable or does not exist.< /p > 

 Post Query in index.php:

<?php if(have_posts()) : ?>
<?php while (have_posts()) : the_post(); ?>
       <div class="some">...............</div>
<?php endwhile; ?>
<?php endif; ?> 

Pagination in index.php:

<div class="nav-previous">
<?php next_posts_link( __( '< span class="meta-nav">← Older posts') ); ?>
</div>< div class="nav-next"><?php previous_posts_link( __( 'Newer posts <span class="meta-nav">→') ); ?>
  </div>  

Activate Option Tree: 

functions.php

add_filter( 'ot_show_pages', '__return_false' );
add_filter( 'ot_show_new_layout', '__return_false' );
add_filter( 'ot_theme_mode', '__return_true' );
include_once( 'option-tree/ot-loader.php' );
include_once( 'includes/theme-options.php' ); 

 Some important tools:

<?php the_permalink(); ?>=link dynamic