I know this is a dumb question and it might not be "conceptual" but, as a self-starter I really want to know how to get connected to some sort of "commercial database"?

I'm recently designing my local gas station utility app for iphone and ipad. I have absolutely no clue of find a relevant database. For example, if I want to make an app for pizza ordering in the great Chicago area. How do I get info (price, menu, location, etc.) of those pizza stores scattered all over Chicago?

Can any one light something for me? I appreciated your help.

**If this question is not suitable here please tell me and I will delete this post.

Thank you.