From PiMyLifeUp:
In this tutorial, we will be exploring how to setup a Raspberry Pi AirPlay Receiver. This tutorial basically involves you connecting your Raspberry Pi to your speakers then installing software so that it becomes recognised as an AirPlay receiver on your internet network. To setup your AirPlay Receiver we will be making use of the open source software called Shairport Sync.
This software allows the Raspberry Pi to act as an AirPlay receiver by implementing Apples proprietary protocols so that it can receive music from those devices.
This will allow you to play music from any AirPlay enabled device to your Raspberry Pi meaning you can use almost any iPhone product and even some Android products with a compatible app installed. A Raspberry Pi AirPlay Receiver is very simple and cost-efficient way to setup wireless speakers without the huge cost of buying a set of wireless speakers. It can easily help you modernise your speakers and help cut the cord.