Moodle is an Open Source Course Management System (CMS), also known as a Learning Management System (LMS) or a Virtual Learning Environment (VLE). Moodle is a free, open-source PHP web application for producing modular internet-based courses that support a modern social constructionist pedagogy. To work, it needs to be installed on a web server somewhere, either on one of your own computers or one at a web hosting company. Lot more information can be obtained from here.
There’s a better chance to grab the books available to learn about this platform from Packt publications, they are providing discounts on both their eBooks as well as printed copies. So you might be interested to know more about this here.