The PHP Developer Guide contains information for developers who want to know more about developing or modifying Adobe Commerce and Magento Open Source components. With this knowledge you can extend or customize any of the existing components. You can also create components that introduce new functionality and distribute them to merchants.
The Adobe Commerce and Magento Open Source applications are made up of Modules, Themes, and Language Packages:
Modules interact with other parts of the application to accomplish a particular business function or provide a feature. A module can contain a user interface for displaying information or interacting with the user. It can also contain application interfaces that another module or code chunk might call.
Themes provide a personalized touch for each Adobe Commerce or Magento Open Source installation by changing the look and feel of the storefront or Admin. Two themes are already available within the default code structure: Blank theme and Luma theme. Refer to these default themes when creating custom themes.
Language packages assist in internationalization(i18n) and localization by providing translations for strings that display on the storefront and Admin.
You must follow a PSR-4 compliant structure when building a module.