Example for form_open() in php

[eluser]shahnawazahmed[/eluser]
hello psp , why we use this code to create forms in php ? we can also do this in Html forms .
<?php
echo form_open('location/to/sumbit/to');
echo "Username : ". form_input('username', set_value('username'));
echo "Password : ". form_password('password', set_value('password'));
echo form_submit('submit', 'Login');

echo form_close();

?>