Sending a Code to an Email Address in CodeIgniter

I'm developing a simple website in CodeIgniter and want to start with an Introduction Page (which I have completed) and for those users interested in registering it moves to a page for the user to (1) Insert & Submit an email address which then sends an automatically generated 4 or 5 or 6 digit code to the email address and then moves to a page for the user to (2) Insert & Submit the code, which if correct then moves to a (3) username & password page (which I have almost completed) and when the username & password have been provided to (4) Send the extended username (that is with an integer on the end) & password to the email address, and moves to another page to (5) provide additional details (which I'm in the process of developing).

Can anybody provide me with simple coding for (1) Inserting & Submitting an email address and sending the Code. and (2) Inserting & Submitting the code and moving to the username & password page. and (4) Sending the extended username & password to the email address?

Preferably with CSS & Javascript in the same pages.

And be able to test from localhost.