TYPO3 Explained 

This chapter describes the core functionality of TYPO3 including API and framework configuration.

Including Installations, Upgrades and updates, Troubleshooting for administrators, and Backend User Management

Including System configuration and the global settings.php, TypoScript, the Configuration inspector (readonly), and Feature toggle API

This chapter contains a description of the formal requirements or standards regarding coding that you should adhere to when you develop TYPO3 extensions or Core parts.

Learn how to write site packages and other custom extension with or without Extbase.

General PHP architectural strategies in TYPO3 core development and best practices for extension developers.

This chapter describes some typical risks and advises how to protect a TYPO3 site in order to ensure it is and stays secure and stable.

This chapter goes into details about automatic testing: Writing, maintaining and running them in various scopes.