Obviously, the terminal must know at least the IP address or the domain name of the "website"

Beyond that depends on what interface you provide between the "website" and your "terminals":

If you are just using a "raw" socket interface, then it's entirely up to you how you implement this!

If you are using HTTP, the Client need only issue GET and/or POST Requests to the Server, and the Server's response contains the required information: GET is a simple request; POST also allows the Client to supply data to the Host in its Body. You could also carry information in the HTTP Headers by defining your own cusom headers...

I had made my terminal capable of using TCP/IP protocol what network layer should come above it ?

You need to write a layer (or layers) above the TCP/IP protocol - not below it!

That could be something entirely of your own devising, using just the "raw" IP sockets;

Or, you could use HTTP;

Or something else!

how to implement that ?

You need to decide what first, before you can think of how!

where to get help from about "terminal to call a public website"?

You have plenty of links already!
Go back and review all the links you've been given so far.

Also, look at the SiLabs website - they offer a complete TCP/IP development kit.

One more time, those tutorials:
http://www.frostbytes.com/~jimf/pap...nsock.html
http://www.frostbytes.com/~jimf/pap...ckets.html
http://www.jmarshall.com/easy/http/

See also: http://www.8052.com/forumchat/read.phtml?id=147686

i think solution is Http protocol

Yes, it is quite possibly a solution - whether it's a good solutions for your specific requirements is impossible to tell without you giving full details of those requirements!

i have seen that also but not able to get the solution

You need to implement an HTTP Client in your "terminals", and your "website" must be able to handle & respond to the requests from your terminals.

if there is any doc or link or code that can help me out please help!

Have you studied the HTTP tutorial yet?
Have you looked at what's available from SiLabs?