cake php use of table relations

Whats the usage of creation relations like

 var $belongsTo = array(
        'UserType' => array(
            'className' => 'UserType',
            'foreignKey' => 'user_type_id',
            'conditions' => '',
            'fields' => '',
            'order' => ''
    //The Associations below have been created with all possible keys, those that are not needed can be removed
    var $hasMany = array(
        'UserOpenid' => array(
            'className' => 'UserOpenid',
            'foreignKey' => 'user_id',
            'dependent' => true)

What if i added a table which created in the sense of "belongsTo", in "hasMany"?
Any error occurs.
How cake uses the relationships specified in the model?