WP WordPress Theme Development

Build classic and block WordPress themes from scratch: the template hierarchy, The Loop, the_title() and the_content(), template parts, menus, the Customizer, child themes and theme.json.

Lessons

1 What a WordPress Theme Is 2 Setting Up a Local WordPress Environment 3 Theme Folder Structure and Required Files 4 The style.css Theme Header 5 The Template Hierarchy 6 The Loop: have_posts() and the_post() 7 Template Tags: the_title() and the_content() 8 Dates, Authors, Categories and Tags 9 header.php, footer.php, wp_head() and wp_footer() 10 functions.php and after_setup_theme 11 Theme Features with add_theme_support() 12 Enqueuing Styles and Scripts 13 Navigation Menus 14 Sidebars and Widget Areas 15 Template Parts with get_template_part() 16 Custom Page Templates 17 Single, Archive, Category and Author Templates 18 Templates for Custom Post Types 19 Featured Images and Image Sizes 20 Pagination 21 Custom Queries with WP_Query 22 The Comments Template 23 Search Results and 404 Templates 24 The Theme Customizer API 25 Escaping and Security in Themes 26 Making a Theme Translation-Ready 27 Child Themes 28 Block Themes and theme.json 29 Block Templates and Template Parts 30 Testing and Releasing a Theme

What a WordPress Theme Is

WordPress Theme Development Lesson 1 of 30 ~3 min read

Overview

A WordPress theme is the set of template files, styles and scripts that decides how your content looks — while WordPress itself stores the content and a plugin adds features.

That split is the single most important idea in this whole path. Posts, pages, users and settings live in the database and belong to WordPress. A theme only presents them. If someone switches to a different theme tomorrow, their content must still be there, intact. Anything that would vanish with the theme — a custom post type, a shortcode, a contact form — belongs in a plugin, not in your theme.

What a theme is responsible for

A theme controls	A theme should not control
Page layout, typography, colours and spacing	Custom post types and taxonomies
Which template renders which URL	Shortcodes your content depends on
Navigation menu locations and widget areas	SEO data, analytics, contact forms
Featured image sizes used by the design	Anything a user would lose by switching theme

The WordPress.org theme review team enforces this rule — it is called plugin territory — and following it from day one keeps your themes portable and your clients safe.

How WordPress loads a theme on every request

The visitor requests a URL such as /2026/10/hello-world/.
WordPress boots: wp-config.php connects to the database and loads core.
Active plugins load, then the active theme's functions.php runs.
WordPress parses the URL into a query — "a single post with this slug".
It runs that query against the database and stores the result as the main query.
The template loader walks the template hierarchy to choose one file, such as single.php.
That template runs The Loop and prints the HTML the visitor sees.

You will meet every one of those steps in this path. Steps 6 and 7 — choosing a template and printing content with tags like the_title() and the_content() — are the heart of theme development.

Classic themes and block themes

WordPress currently supports two kinds of theme, and this path teaches both.

	Classic theme	Block theme
Templates are written in	PHP files such as `single.php`	HTML files of block markup such as `templates/single.html`
Design settings live in	`functions.php` and CSS	`theme.json`
Edited visually in the Site Editor	No	Yes
Best for	Learning how WordPress works, custom PHP logic, existing sites	New sites that clients edit themselves

We start with classic PHP themes because they show you exactly what WordPress is doing. Once you understand the_title(), the block equivalent  makes immediate sense. Lessons 28 and 29 cover block themes properly.

What you will build

Across this path you will build GDC Starter, a complete classic theme with a blog, single posts, pages, custom page templates, menus, widget areas, a customizer setting, translation support and a child theme. Every lesson adds to the same files, so by the end you have a theme you understand line by line.

Tip: Keep the WordPress Theme Handbook open in a tab. When this path says a function exists, the handbook is where you check its full parameter list.

Practice

Open any WordPress site you have and switch between two themes. Notice that every post survives the switch — that is the content/presentation split in action.
List three features a client has asked you for in the past. Sort them into "theme" and "plugin territory".

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