How to post a product in your application

How to post a product in your application

The problem is that I have an IOS application which you have to register
to see the available products. (products like in ebay)
I need to know what is the best way to build a system that any user can
upload a product and has his products in a pool of products.
every product should have it's own data and about 5 images (so every
product is a row in the DB) How do you save the images in the server and
knows which image connected to which product? How to save the user's
products in the server?
The question is what is the best way to build such thing?
I'm using Objective-C and PHP (as server)