This document provides an introduction to creating custom themes in AtoM by overriding relevant theming files, registering a plugin, customizing the home page and other elements. It outlines how to create a basic theme structure and configuration class, edit CSS and template files, override modules like static pages and information objects, add a footer, and modify elements like the two-column layout, user menu and more. The goal is to give developers a starting point for creating their own themes in AtoM.