Beginning Creation of Mobile Workorder App

I have the idea to build a mobile workorder app, that will basically allow selection from a customer list, be able to add items(and associate them with that customer), and automatically create a form for a selected end user to fill out(telling what items were used, etc)

I know I need to know SQL & PHP to achieve this. I have learned enough SQL to create a database for customers & items.

What do I need to do to link these together in such a way in the backend so that I can link them together on the front.

All in all, I am a total newb, would love to know a resource that is all in one teaching you to link php with sql.

Thanks to everyone!