User login and session data [how to ?]

[eluser]PorkOne[/eluser]
Hi
I know that this topic is coming back very often, but I didn't found clear answer for my question.

How to keep (secure) user's data after login without any additional libraries, using only standard CI components?

The first thing is to keep session in the database and encrypt cookie. I did it and I have created table 'sessions' where all session's data are stored.
But... new session automatically starts every time user open my page and this information is stored in the database, but there is no place for user's custom data, such as login, name and any other. Maybe I don't understand how this should work...

Is it possible to start session only for users who can log-in into my page (not for all)?

Can anyone try to explain me what should I do to keep (in secure way) user's data?

I'm hope it's enough clear... and sorry for my english

Thanks