Passcode or PIN code

I am looking for some information on how to change password into a pin code or password.

Can anyone know anything that can be used to build this kind of functionality for a website?

The idea to make a website more like an app. For security, there would be a required Google 2FA and hidden captcha.

So the idea is this:
1. User enter his email
2. Enters his passcode – 6 digits – (twice would be cool)
3. And creates Google 2FA key
4. Account is created
5. User receives the email with all his information
6. Login with email + passcode + 2FA
7. Secure and simple to remember ??