There are a couple of ways to tune your guitar. You can use an electronic tuner or you can tune your guitar by ear. I recommend you use both but practice tuning by ear everyday so you get good at it and can do it quickly. Use an electronic tuner so you can get used to what the exact pitch is. There are many times where you may not have your tuner and times when your playing and your guitar may go a little out of tune, from bending notes or using your vibrato bar, and if your familiar you can tune it back fast by ear. When tuning a string always take the pitch lower and tighten the string up to the pitch because its less likely to go out of tune then if you tighten down to the correct pitch.