Need some help with a Smarty php script

I have a working script that has its own login/register and everything is working. I am trying to integrate FB login into the script using gigya and am able to populate user data in the dB but I am unable to make session integration in smarty templates session_start() $_session['user_id']=$DB['DB value'] All I need help is to register session same as login and register page. On the main page I have a link to login using FB credentials, after we click on FB login the user redirect on test page, I am just trying to login this user as normal process that already exists. This should not take more than 5 min for someone familiar with smarty and has worked on log in integration.