I've tried many Apps and I recommend two of them to get you started.
The first one is called "Waking Up". Join Sam Harris—neuroscientist, philosopher, and New York Times best-selling author—as he explores the practice of meditation and examines the theory behind it.
The second is called Head Space and was impressed with it's simplicity and results. It's very simple and effective way to relax and develop your focus, and more than 5 million people have already tried it.