STEPS
TOOLS
Go to the app store and search chromatic tuner.  This is the list it pulled up for me.  I have found Cleartune to be the best. However there are a lot of options out there.  Install app.
Here are the ratings for the app I use.
Grab your instrument!      Below  is a great resource to find the tuning of almost any instrument. http://tunings.pbworks.com
Start Tuning.  Standard guitar tuning is: bottom (fat string closer to your head also #6) to top (the thinnest string closest to the ground also #1).   E A D G B E      Have fun
 Guitar or other instrument
 Chromatic Tuner app

How to tune guitar and other instruments with an iphone

You can tune most instruments with the iPhone, eliminating the need to buy another device.