Difference between www. & Non www?
 

Let me know the importance of www. Also is there any problem coming not using www.

Your domain name does not include the "www" - that part of an address is known as the sub-domain. It points to a folder on your web site. You can have multiple sub-domains, all registered under the same domain. So you could have "www.example.com," "discuss.example.com," and "blog.example.com," all registered as "example.com."