How can we add customize the data model? please give me the brief explanation or the document if any
If you are asking about the database data model, then it's simple: you cannot change it.
If you are asking about the conceptual data model, in other words, how Windchill/Integrity is used by end-users, then it's an enormous subject: how to create/modify fields, item types, workflows, triggers, permissions, queries, etc., etc.
You need a lot of training for that and there is almost no usable documentation. I suggest you talk to the system administrators in your organization, if you have any, or PTC Services.
I am talking about the conceptual like Thing Template etc ..Can you pleas explain in details
Sorry, no, I cannot explain in detail such a vast question. That's what I was trying to explain before: I believe you need training.