How to: Registration and Login

I'm building a new website that, for the first time for me, will require registrations and logins for a forum it's hosting. Here is what I see as the process:

1. A person comes to the site and can browse it just like any site.
2. He/she can go to the various forums and read what's there.
3. If he/she wants to either answer a question or create a question (topic) he/she will have to login.
4. If the person is not registered, he/she will have to do so.
5. Once registered, every time the user visits again login will be required to participate in the forums.
6. The user will have to be allowed to change his/her email address.
7. The user will have to be allowed to unsubscribe.

I'm not sure how to set this up. I'm using WP 4.1.1 using the Divi theme. I'd appreciate any information on how to set this all up or links to information that will explain how to do it.