The TYPO3 system is multi-layered. The backend and frontend user interfaces sit on top of the application layer, which in turn sits on the infrastructure layer. The webserver, database and PHP in the infrastructure layer are prerequisites for running TYPO3.
TYPO3 Core primarily consists of the API (Application Programming Interface), which defines a framework for managing the project content. The base features of the API include content storage, user permissions and access, content editing, and file management. These features are delivered via system extensions that use the API. All of the content is stored in a database that TYPO3 then accesses via the API.
Extensions are clearly confined code additions, such as plugins, backend modules, application logic, skins, and third-party apps.
The most important thing to note is that everything is an extension in TYPO3 CMS. Even the most basic functions are packaged in a system extension called "core".
The TYPO3 Core framework interacts with system and 3rd party extensions via the TYPO3 extension API.
The core and extensions interact with each other seamlessly and operate as a single, unified system.
User interface layer¶
The backend is the content-creation side. It is the administrative area where you manage content and configuration based on the extensions that are installed.
The frontend is the content-delivery side. Typically a website, it is the meeting place for templates, CSS, content, and logic from extensions, delivering your project to the world. The frontend doesn't have to be a website, it could be a native mobile application, a web application built in a frontend framework, or an API to interface with other systems.
A basic installation¶
To follow this document, it might help to have a totally trimmed down installation of TYPO3 with only the Core and the required system extensions at hand.
The installation process is covered in the Getting started Guide. You should perform the basic installation steps and not install any distribution. This will give you the "lightest" possible version of TYPO3.
In your basic installation, go to the Admin Tools > Extensions module. You will see all extensions installed by Composer are activated by default.