I am new to XML and need headstart for a car hire website which requires XML connectivity with its partners. So please help understand what do I need to know to start it?
Thanks for help!

You need to know

- where and how you host your data
- what api your partners provide or need
- how to process / generate / query / store XML data

As you are building an internet service you could think about using a platform as a service in the cloud. Then, you don't have to take care for

- administration
- scaling as you grow
- replication
- backups
- automatic failover
- disaster recovery

Also, as you are building a XML based service you should use a programming language that can deal with it best. Most people are tempted to use a programming language like PHP, ruby, Java, or ".NET" to process XML and store the XML data in a SQL database. If you don't have plentiful of time and money to waste: don't do that because you have too much overhead for design, mappings, parsing and marshalling of XML data. It is much more efficient to use XQuery for example (From my experience I would say that you can safe around 80% on average for code, design, testing, maintenance ... ).

Check out for example: http://www.28msec.com. They provide a database in the cloud where you can store XML natively out of the box. Plus, you can implement complete websites or REST apis only.

thanks so much for the help. will try that!