How do I get this iTunes song on an Android device?
In recent years, Apple has sold songs on iTunes without DRM. You can convert them to other formats pretty easily, then just drop it onto your Moto X using a USB cable (Or even just email it to yourself, then download it using your email app on the phone).

Music stored on the phone should automatically be added to your "On Device" library in the Play Music app. I would recommend making sure you save it somewhere standard like /sdcard/Music/ for your convenience.