I suggest that you visit your local book store and get a book for php and mysql basics. I've been programming with php for 10 years now and those things you are planning on doing feel daunting to me too Learn some basics first, do a simple program. For example user creates an account, logs in and asks for a price of some item which is then searched from the database and returned for the user - something like that. Just a simple one form query.
Also if you are unfamiliar with terms like xhtml,css, javascript you will need to take a look on those too.
http://www.w3schools.com/ is a good place to look into if you havent already and simply googling "php mysql tutorial" will give you more sites if the Internet is what you prefer.