Thought I would throw your way some good reference material. If you don't know about php.net look them up and then do a search for the date() time() mktime() and strtotime() functions. And as a database is needed you can look up the mysql functions. They have tons of examples and user input, for all the php functions, that can be of great help if your just getting started.

Even after 10+ year of web design I always am looking things up on their site.

Also I hope your web host has phpmyadmin for you to use as it will make the initial setup of the MySQL data base a breeze as well it has some nice features that may help you learn to work with MySQL.

After that google, the number of times I have searched for "php somefunction" to find good examples of how to use some functions is innumerable.

As far as using AJAX, I would say if your not proficient with both PHP and Javascript and debugging them then steer away from it for now.

What your trying to do is fairly straight forward. I believe my first php was of a similar nature. I think as recent as a few months ago I used that script (obviously updated for php changes).

After looking up those functions and you have something as far as working code that we can look at I am sure many here can help you in much more detail.