- How list/library data stored in SharePoint
- How/Where Document are saved in SharePoint
- Where configurations are saved in SharePoint
Everything is stored in database tables. You have one or more content databases setup for each application. Each Content Database contains the content for one ore more site collections. This includes lists, documents, version, workflow content, permissions, site information, etc.
The configuration information is stored in the Configuration Database, and there is one per farm.
If you have the full version of server installed you may have additional databases to cover the extended features like search, user profiles, etc.
In case it needs to be said, it is fine to understand the underlying architecture, but it is a bad idea to try and interact with the tables directly. You will want to go through the API or web services to interact with the content and system.