PHP Composer is a dependency manager. It manages the dependency of PHP packages in your application. Using composer you can pull the required library and dependencies and manage them in one place. The concept of a composer is similar to npm in node.js and gem in Ruby.
Composer will solve these three important problems.
Dependency resolution for packages. Autoloading packages. Update all your existing packages
Dependency resolution: Suppose you have downloaded any PHP framework or library. Now the framework you have downloaded depends on an external library such as guzzle and JSON-schema etc to work. Similarly, guzzle needs Symfony’s event-dispatcher and the list goes on. Composer handles these dependency resolutions automatically.