Creating a mobile phone app to use in restaurants Don't know where to start?

Hi! I am doing a voluntary projet which I am not too sure of how to go about doing. I have to try and create an application which users can use at a restaurant to order food and drinks using their phone as opposed to ordering with a waiter. The restaurant must be able to update their menus and details. So I am planning to have a web front end for the restaurant to update menus and details with simple forms which update to a database. However I am not to sure about the mobile end and how to write to a database as I have never done this. What databse can you use, could you use something like MySQL. What are midlets? How difficult is this to do? Hope this makes sense. I have fairly basic knowledge of Java but am prepared to learn. I will appreciate any pointers?