store session variable in a table

hi,can anyone tell me how a session variable can store in table,

Do you mean change from storing sessions in a cookie to storing in
your database?
Or do you mean something to do with using the session?

no, suppose that there’s a person who has logged in to a site

and when he fill a form so the data should be stored in a table

with his user id which has stored in his session. so how can

i store it.

You could access the session in the controller at the time the user
submits.
Depends on what your authentication system does.
For instance it might be session[:user]. So you have to do something
like
  user=User.find(session[:user])
or
  User.exists?(session[:user])
to verify the user id is valid.
There may be helper methods which come with whatever plugin or system
you're using
so you should check them out.

If you don't have a system, there are quite a few.
acts_as_authenticated, restful_authentication to name 2.
You'll need to install one of them and read how to use it.

thank you very much,now i can understand what should i do