You can look at chords as the building blocks of a song. There are lots of different chords and you can try to learn them all. But to have an understanding about the way they are built can make it easier to memorize them or make your own chords and voicings and to use them in your songwriting.

The basic form of a chord is a triad, which means it consists of three notes. The root, the third and the fifth. There are major and minor chords. Major can be described as happy sounding and minor as sad.
Whether it’s a major or minor chord depends on the third. A major third interval makes a major chord and a minor third interval makes a minor chord.
Which makes the third the most important note of a chord, because it all depends on the third if it’s a major or minor chord. Sounds logical?
So that’s the basics, you can add different notes that will add to the flavor. It’s like a pizza margherita, the most basic pizza. You can add different cheeses, meats and vegetables depending on which flavor you want.
It works the same with chords, you can add notes to your triad which will give a different flavor to your chord. Depending on the feeling you want to create. You can add notes from the melody, which will enhance it in the arrangement. Or you can you can use a certain chord because that stands for a certain type of mood you want to create. Maybe the ‘G7/b9’ is your pizza prosciutto.

Of course you don’t have to use the extra notes, there are lots of possibilities with just the three notes of a triad. And you can use that in the arrangements of the songs you play. Especially when you play in a band with a lot of different instruments. Maybe you have a bass guitar, two guitar players and a keyboard player. If you all play the full triad it can sound muddy. You have to leave space for the other instruments, as a guitar player you can decide to only play the essential, which is the third. You don’t have to play the root, because that’s already done by the bass player. The keyboard player can play the full chord in the low register and you can add the third on top of that. Or you can play the full chord higher up the neck or just the third and the fifth. On the guitar you can play the same chord on different places on the neck and they will sound differently. That’s something you can keep in mind when you have two guitarists and you both have to play the same chord. When you start to experiment with that, you will find that there is much more space for the vocalist or other instruments and that it sounds much more transparent. Of course it depends on the type of music you play. In rock and metal it is common to play just power chords on the guitar, which is only the root and the fifth. So that’s neither major nor minor. They’re very heavy sounding chords, but that’s what you want. It usually doesn’t has to be that subtle when you play that kind of music. In a pop song or ballad on the other hand you might want a well balanced arrangement. Now that you know a little about how it works you can use it in your own songwriting and playing.
In the example on the right, there are a few inversions for a D chord. You will probably recognize the different shapes, if not, now you know. And you can apply the same idea for any chord. Good luck.