Magento - Module INSERT,UPDATE, DELETE, SELECT code

I created a module and want to used core write and read function to insert,update,delete or select database value with condition, how can I do it without using SQL? Example: $customer_id=123 Model=(referral/referral)

SELECT

 $collection3 = Mage::getModel('referral/referral')->getCollection();
    $collection3->addFieldToFilter('customer_id', array('eq' => $customer_id));
    foreach($collection3 as $data1)
    {
    $ref_cust_id.= $data1->getData('referral_customer_id'); 
    }

INSERT

$collection1= Mage::getModel('referral/referral');
$collection1->setData('customer_id',$customer_id)->save();

DELETE,UPDATE(with condition)=???