How do I create, write, and read session data in CakePHP?

can anyone give me an example on how to create Sessions and write data to it. I've seen syntax on how to write data to a session using write command. But how to create a session and retrieve the values in it.

In my application, I have two data, form_id and user_id that needs to be used in all the page requests. So how do I save it as a session variable and use it across the application?

EDIT

function register()
{
    $userId=$this->User->registerUser($this->data);
    $this->Session->write('User.UserId',$userId);
    //echo "session".$this->Session->read('User.UserId');
    $this->User->data=$this->data;
    if (!$this->User->validates())
    {
    $this->Flash('Please enter valid inputs','/forms' );
      return;   
    }

$this->Flash('User account created','/forms/homepage/'.$userId);            

}   

How to use the session variable 'User.UserId' instead of $userId in $this->Flash('User account created','/forms/homepage/'.$userId);

And can I use this variable in all my view files,because in all the page requests I also pass the userId?

EDIT 2

I have 2 controllers,user and form. I write the userid to a session variable in the users_controller. I have a view file called homepage.ctp,whose action is in the forms_controller. Now how can I use the session variable defined in the users_controller in the homepage? Sorry if I am asking silly questions. I went through the cakebook,but my doubts weren't cleared. I'm also trying trial and error method of coding,so please help me.

EDIT 3

I have a session variable 'uid' which is the user id in the home page action of a controller.

       $this->Session->write('uid',$this->data['Form']['created_by']);

I need the same variable in the design action method of th