If you are going to write a song, you will have to choose a key for your song, and the biggest choice is making it either major or minor. If your song is happy, funny, or danceable, then you might want to pick a Major key (i.e. C Major). If your song is sad or contemplative, you might want to pick a minor key (i.e. A minor).
On this website I will capitalize the word “Major,” not because it is proper English grammar but because in music notation we represent “minor” with a lower case “m” and “Major” with a capital “M.”
Note: If you are just learning a new instrument or are new to making music, then just play the chords and notes you already know, and try to figure out the name of the key later. If you want to learn some of the technical details to improve your musicianship, then read on!
The chords that fit together in a Major key, taking the key of C for example are:
Note: The small “m” stands for “minor.” There is a difference between the use of the word “minor” when describing the key of the song and the use of the word “minor” when describing a chord. In this case we have a Major key, but inside of it are various Major and minor chords.
The “Bo” is a representation of “B diminished chord,” and we can get to that later.
The chords that fit together in a minor key, taking the key of Am for example are:
Compare the chords in the key of C Major and of A minor. Notice they are the same chords but in a different order. The difference is that the key of C Major can sound happy whereas the key of A minor can sound sad.
There are a zillion resources online related to music theory. Take some time to learn a little bit at a time as you go through life.
You also need to take into account the range of your specific voice, if you are going to be the primary singer of the song. Every singer has a sweet spot – a key that works better for him or her.
If there is a song you really love singing along to, then find out what key it is in and write your songs in that key!