Is it fine to draw diagram to Web browser -> Server scenarios ?
Maybe.
Can i draw diagram for the socket connection ?
Do you mean "can the socket have a lifeline in my sequence diagram"? Yes, it can. Sequence diagrams describe verbs by capturing interactions by objects. You can describe how to create a socket connection in one of them, because "create" is a verb. The connection itself will be one of the participants.
Can i draw sequence diagram for intermediate processes in the TCP
server ?
Maybe. Which ones? Why?
You sound like you keep asking permission. You can do anything you like. Whether it's useful is still to be determined.
What are the rules that i obey on ?
There are no rules, except those built into the diagram. There are no UML police that will come to get you for breaking imaginary rules.