Graphics for Retina Display!!!

Hello everyone, I'm Manas, 15 year old, game and app developer from India. Currently I'm engrossed in making an iOS game on Unity Engine. I started building it but as soon as I tested it on my iPad, the images were blur. I'm not much into graphics, nor am I getting proper resources or guides to show how to make images or graphics compatible with Retina display. I'm using an early 2014v MacBook Air with Unity 5.0.2f1. Also Adobe Photoshop, Illustrator and GIMP. Any other software for creating high resolution graphics would be appreciated. Your help would greatly be appreciated. Thanking you in anticipation!!