Compare XML, XML Schema To Database
XML is designed to store, carry, and exchange data. If you are familiar to database, then, think about tables. They are both data containers.
An XML schema describes the structure of an XML document. Well, you know what table structure is, don't you?
XML Schemas are written in XML. If you know SQL Server, perhaps you have noticed that some tables named sys* are used to describe the table structure.
Now, you've found that XML and XML Schema are not difficult to understand. They are another way to describe and store data. They are web babies.