First of all, it sounds like you don't have any graphical interface for MySql currently. Do you have phpMyAdmin? If not, GET IT!
http://www.phpmyadmin.net/home_page/

phpMyAdmin is a PHP browser-based MySQL Administration tool. You can create databases, table, columns, edit current data, get lists of data, import, export, etc. It's really nice, and it's free. Installing it is *easy*, but depending on your exact server setup, you may run into small issues. Just follow the documentation, and keep banging until you get it working. You can use it as your admin tool to add users into your table -- that is if only you need to have this privilege. You don't want to give anyone else access to directly modify your database and tables.

If you want a tool to help you build web forms to your MySQL data, look at Databik. This is the second post in which I'm "recommending" this tool, but I've never used it...so I hope somebody provides some feedback regarding it. It looks like a solid, simple, tool.
http://www.dadabik.org/index.php

I have personally authored a PHP class to handle Session Management & Password Protection. I wrote an article about it.
http://www.tgreer.com/class_session_php.html

The class includes a sample login.php page that works with the session mgmt class. You'll need to insert your own database logic to test authentication.

For working with your database in PHP, I've authored another class that I think makes working with MySQL very easy (PHP already makes it really easy!) My class provides a common interface to multiple databases, so if you ever end up changing databases, it's not difficult to migrate your code. My class_db also allows you to cache data if your database resources are limited. The caching mechanism is transparent to your code. Probably more than you need, but the article & code can teach you about working with MySQL in PHP.
http://www.tgreer.com/class_db_php.html