You are browsing the documentation for Symfony 4.0 which is not maintained anymore.
Consider upgrading your projects to Symfony 5.2.
Composer is the package manager used by modern PHP applications. Use Composer to manage dependencies in your Symfony applications and to install Symfony Components in your PHP projects.
Since this article was first published, Composer installation has improved a lot. Therefore, the original contents of this article have been removed and you are encouraged to install Composer as explained in the official Composer documentation.
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.