About component file structure | Magento 2 Developer Documentation

One of the first things you can do to get started with component development is to understand and set up the file system. Each type of component has a different file structure, although all components require certain files.

In addition, you can choose the component root directory to start development. The following sections have more information.

Root directory location

A component’s root directory matches the component’s name and contains all its subdirectories and files. Based on how you installed Magento, you can put your component’s root directory in one of two places:

<Magento install directory>/app: This is the recommended location for component development. You can set up this environment by Cloning the Magento 2 GitHub repository.
- For modules, use app/code.
- For storefront themes, use app/design/frontend.
- For Admin themes, use app/design/adminhtml.
- For language packages, use app/i18n.
<Magento install directory>/vendor: You will find this location for installations that use the composer create-project to install the Magento 2 metapackage (which downloads the CE or EE code). You will also find this location if you install Magento by extracting the compressed Magento 2 archive.

Magento installs third-party components in the <Magento install directory>/vendor directory. But we recommend adding your components to the <Magento install directory>/app/code directory. If you add your component to the <Magento install directory>/vendor directory, Git will ignore it because Magento adds the vendor directory to the <Magento install directory>/.gitignore file.

Required files

The following files are required for all components:

registration.php: Among other things, this file specifies the directory in which the component is installed by vendors in production environments. By default, Composer automatically installs components in the <Magento root dir>/vendor directory. For more information, see Component registration.
composer.json: Specifies component dependencies and other metadata. For more information, see Composer integration.

Each component has an additional component-specific required file:

Component Type	Required file	Description
`magento2-module`	module.xml	This file defines basic information about the component, such as component dependencies and version number. Magento uses the version number to determine which schema and data to update when executing `bin/magento setup:upgrade`.
`magento2-theme`	theme.xml	Describes the Magento theme. File specifies a theme name in the `title` node, a parent theme (optional), and a theme preview image (optional) in the `media/preview_image` node.
`magento2-language`	language.xml	Declares a language translation package.