what is the importance of xml schema?

hi I have created an XML file but now I have to create an XML schema.Can you guys tell me the importance of schema and the meaning of the line code.

<xs:schema xmlns:xs="http://www.abc.org/2010/XMLSchema">

from where would I get the url just like above?

The schema is used to validate a document, and to assist people/programs from creating their own versions of XML according to the schema.

If your document is supposed to be an XML schema, then it must start

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

You can use a different namespace prefix if you like (some people prefer "xsd" to "xs") but the namespace URI must be exactly as written. It's a URI not a URL - a symbolic constant that identifies the XML vocabulary as being the XML schema vocabulary. If you use a different namespace, then it's not an XML schema any more.