How does createrepo work. How does yum understand parse its files. A conceptual explanation

Createrepo creates some informational files that can be used by yum tool while fetching data from a reposiotry. The files are filelists.xml,repomd.xml etc. the below tutorial explains the complete yum working. How does YUM work?

I can't provide a complete answer to the entire flow of yum, but the following page describes createrepo and the rpm-metadata provided by createrepo.

http://createrepo.baseurl.org/