The iPhone 5s is the only product currently with the A7 in it. Simply put the A7 is a faster 64bit processor. What that does is let the phone load, render, etc quicker then the older A6.
The iPad 5 will have an A7X chip in it. And the iPad Mini 2 might also have an A7X chip in it.
As far as the iPhone 6, it's anyone's guess. But it will more then likely have a chip called the A8. Which will be a more powerful version of the A7.