Retrieving values from client

Hey,

i just got a few short questions regarding to the usage of vaadin.

I developed a small quiz-game just to learn the java-basics a while ago and did some other projects until yesterday.
My idea for now is to update the quiz-game to a local party game, which can be controlled by mobile phones.

To do so, i created a small website in vaadin with 4 Radio-Buttons and a single submit-Button; as my first question is following now:

Is it technically possible to get different “instances” of the website? I´m talking about something like a variable that is increased(just for the newest user) by 1, to identify the user giving the answer. By clicking the submit button, the selected answer and the unique user-id are provided to the java-sided part.

I read that it is a bit difficult to get values from the client-side to the server-side, but i did not understand how to do it properly.

Can you maybe give me advice how to do it? (I´m not talking about written code, just how (and which!) function are the best to get the values from the clients.

I hope you can understand what i was trying to say, because i dont speak english very well…

Best regards,

Julian