I have spent a lot of time looking for tutorials about Composer, and most of them concentrate only in how to install and the basic usage of the dependency manager frameworks. Which is something you find on the Composer official web site. This represent a problem if you want to use your own custom private dependencies and classes.
But very few of the tutorials explain how to use your own code, or add them into the composer.json file to take advantage of the autoload method. But do not fear, I found a great tutorial that cover all, the PHP Composer Tutorial by Lamin Sanneh.
This is a youTube playlist that consist of 19 videos, they should play automatically once you trigger the play button, so relax, sit down and enjoy.