Composer is a command-line tool that helps you manage your application dependencies. It automatically fetches packages, resolves dependencies and is easy to configure. [...] Currently, Lithium doesn't provide Composer packages out of the box, but it's easy to write one.
He starts the post with an introduction to using Composer for those new to the tool, then moves quickly into setting up your "composer.json" file to pull in the Lithium updates from their github account. Additionally, he shows how to add a dependency for twig in the "require" section and pull it down at the same time (with dependencies).