Question

I want to get to know how I can transfer data easily between 2 iPhones, over wifi. I would like to know if I could do that without having a server or database, but within an app (so without using email).

Answer 1

Game Kit has support for Peer-to-Peer-Connectivity and is, despite the name, not only usable for games:

The GKSession class allows your application to create and manage an
ad-hoc Bluetooth or local wireless network, as shown in Figure 1.
Copies of your application running on multiple devices can discover
each other and exchange information, providing a simple and powerful
way to create multiplayer games on iOS. Further, sessions offer all
applications an exciting mechanism to allow users to collaborate with
each other.