I need to create a PHP register and login form for my website so that only those users using my system can log in after they've registered.

Their details will be stored in a database which I have yet to set up.

I am clueless with how to go about this, I have not used PHP at all. Do I need to identify the relationships/tables in my database first (MySQL/PHPMyAdmin) or can I build this register box and login box first?

Can somebody please explain how to go about this?

Thank you.