Let's start with some basic advice for building extensions. Once you get familiar with TYPO3 extensions, you will notice that there is a ready-made solution for just about any problem. So before you create your own extension, check to see whether there is one already in existence that will solve your problem. The installation of any extension is made incredibly simple using the extension manager. The entire system of extensions is very well developed in TYPO3 and consists of the following components:
Extension API: This is the interface which you use to integrate extensions into TYPO3.
Extension Manager: This back-end module handles installing, updating, and deleting extensions (more about this later).
Extension Repository: This is the central contact point for extensions—developers can upload their extensions and users can download them and get information on individual extensions.