DB

I am trying to structure a database for optimal use. But I have no idea how to make that happen. Here is what i will have A category which will have many products and a count for each one of those products For example Restaurants will be the category and the products will be the computer system, cash register and each one of these products has a count so maybe there will be 2 cash registers and 3 computer systems and so on. Another category might be a bar, which might or might not have the same products. Then the user has the option of choosing a 2 restaurant package which might have a discount rate for getting all the products. anyone knows how the DB structure should be ?!