Playing in tune will sound more pleasant than playing out of tune. So your practice time will immediately get more enjoyable.
You get to know your instrument a bit better. Depending on the tuning methods you will get to know the names of the strings and what notes are on additional frets of some of these strings.
You will train yourself to recognize pitch. This goes far beyond discerning whether a guitar is in tune. This skill will help you to recognize pitches and chords played in all songs you will hear. It will help to deepen your enjoyment of music in general. And for this benefit you don’t have to do anything beyond the practicing you do anyways. By playing in tune you play and hear sounds that have a certain relation to each other. By listening to playing that is in tune you strengthen your ability to differentiate the pitches.
You want to have those benefits? They are quite easy to get. I will propose two ways to tune your guitar.
Method 1 – The electric tuner
This is the easiest method. Buy an electric tuner or use an App for your mobile phone. Using it is quite simple. Usually you start the device and are ready to go. Then you pluck the thickest string and check whether the device is telling you this is in tune to the note E (if you are using a regular 6-string guitar in standard tuning). If it isn’t in tune follow the string all the way to the neck. One of the turnable knobs should be connected to the thickest string. Turn this knob and check with the device whether the pitch gets closer to the E or farther away. Once the tuning device shows you that the string is in tune got to the next string. The remaining strings should be tuned to A, D, G, B, E respectively from thicker to thinner strings. This may take a minute or two when you do it the first time after a long while, but with some experience this will not take longer than ten seconds.
Method 2 – The fretted method
This method is a bit harder to do, but the benefits are greater, too. We use the property that the note of the open strings can be found on the other strings. If we want to tune the string next to the thickest string, all we have to do is play the fifth fret of the thicker string and then the open string next to it. Then we change the pitch of the open string until both notes are the same. We can then go on to tune the D and G string in the same manner. Play the deeper sounding string in the fifth fret and the next string open. Once we get to the B string we have to be careful. The B string is tuned to the fourth fret of the G string. Finally we tune the high E string to the fifth fret of the B string.
The problem here is that one string has to be in tune already. You can achieve that by using another instrument that is in tune already and tune your corresponding string to that note. Tuning forks are another useful device. They are typically tuned to the A note. So you would have to tune the second thickest string to the note coming from the tuning fork.