When we 'submit' the values of the variable using GET method in HTML , How do we take that value and use it in the sketch ?
Have you looked at the complete GET request, as received by the Arduino, when the page is first requested, and when the submit button(s) are pressed? They will be different. The first time, the GET request should look something like "GET / HTTP/1.1". The second should look something like "GET /?num=12&name=Joe HTTP/1.1".
It is not terribly difficult to detect the presence of the ? in the request, and to extract the tokens after it ("num", "12", "name", and "Joe") and to copy the appropriate tokens to the right variables, with any required conversion.