Is there any difference between an web address with “www” and without one?

example:

www.cpwebhosting.net
and
cpwebhosting.net

there is no difference unless you specify this in your DNS

ie www can have an A record which points to a different IP address.

You can think of the www as being a type of alias for the domain name or otherwise where the web portion of the domain name lives.

Thanx alemcherry

how do we set it up so that it will have www,If currently domain has no www

Set up a A record for your domain called WWW.
You need to set up the IP address as the same one that your ste is hosted on, usually the same as the @ record is pointed to.

Well, Does it have any effects on search engine results?

There should not be any affect on the search engine as long as both the www and non-www points to the same web site.

Yup, www is just another subdomain that was popularized by the media. www means “world-wibe web” but anything can be used in it’s place and still be on the world-wide web.

Some companies use www as their public site and just the domain name as their “company internal site” or website map if they have several websites.

It makes absolutely no difference to search engines whether or not you use www or not. However, most users are used to typing in www in front of everything so it might benefit your exposure by using www.

Search engines does not penalize you if you do not use the ‘www’ variant.

Technically, the non-www is the actual site and the ‘www’ version is technically a subdomain but since it is associated with the internet, ie ‘www = world wide web’, it seems to be associated to websites and thus people use that as part of their URL.

Google sees them as two different sites. But in general same thing… Just a preference kinda of thing.