An essential skill in learning the guitar is how to tune your instrument. The strings are under constant tension and will loosen over time. You should get in the habit of checking the tuning every time you pick up a guitar. Remember, if the tuning is off- everything sounds off.
The best solution is to get a tuner. There are several free tuner apps that you can download, or you could always purchase a clip-on or stand-alone tuner. I’d strongly suggest getting both. A tuner will tune your instrument to a standardized pitch (often referred to as Concert Pitch (A=440)). Click here for the Using a Tuner video.
But you will occasionally find yourself without a tuner handy. In this case, you can tune the guitar to itself -tuning each string relative to each other.
To do this, you’ll need to know the names and numbers of the strings:
Put your right-hand index finger on the 5th (A) string and follow it up to its tuner. If your guitar is strung correctly, turning the tuner clockwise should loosen/lower the pitch.