There's a lot of awesome libraries out there that you can use with your projects. What's the best way to manage those dependencies and keep everyone using the same version? Commit them to your repository? Use git submodules?
Try Composer. It's an extremely easy way to document dependencies, lock them down to specific versions, and then help to ensure every developer on the project is using the same versions of the included dependencies.
Learn how to use Composer to manage dependencies and then learn how to share your libraries with others by publishing your own composer compatible projects.