Many websites have areas which need to be only available to people who have signed up, or to people who have paid a fee. I can password-protect as many pages as you need, requiring the user to log in only once. They are required to enter a username and password, which is then checked against values stored in a database. Sessions are used to store the log in information, and I use security checks to ensure that non-members cannot access the membership area.
A signup form on your website will allow people to sign up, giving you all the details that you require. If required, they will also be able to pay instantly through a payment gateway such as PayPal or NOCHEX. On completion of the signup process, they will be given their username and password. This can be displayed on the final page, emailed to them, or both.
All of your members' details will be securely stored in a MySQL database, with the passwords encrypted.
There will be a page on the website for users who have forgotten their passwords. On submitting their username, their password will be reset. Their new password will be emailed to them.