How IP divides to point sub domains [closed]

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I believe that default domain some www.domain.com points to some IP address 123.123.123.123 here when a sub domain is created which points to the same IP address. How the division of IP address works in real time to distribute IP to various sub domains. Do it uses port numbers to each sub domain? or any other method?

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The root DNS server contains an entry called an NS record which indicates for each domain which server to query to resolve names in that domain. That server in turn may further redirect ("delegate") queries for individual subdomains. Read about the DNS e.g. at Wikipedia.

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It sounds like you're asking how a webserver distinguishes between www.domain.com and something.domain.com when both are on the same ip address? It's done by the webserver - Apache uses VirtualHost configuration entries to distinguish based on a combination of IP address and the domain in the http URL.

You can read more about it here: http://httpd.apache.org/docs/2.0/vhosts/name-based.html