What is Music?
While a more poetic definition might be that music is the language of emotion, the simplest scientific definition I could find was: “Music is the arrangement of sounds in time”
And the controls in the above visualization control exactly these three things; arrangement, sounds, and time.
Here's a link of Jacob Collier explaining what music is (in just 2 min) better than I ever could.
“Why am I learning alphabets again? And what is this Home key?”
--> Alphabets
Well, in all truthfulness, there are infinite sounds, each having their own sound frequencies. Sounds made by us, birds, trees, even wind. A lot of sounds aren't even audible to the human ear. But to make life easier, many cultures have standardized 12 sounds for music, which are represented by alphabets, A through G (there are some with ‘#’ or ‘♭’, but essentially they are just a weird way of naming these sounds).
For the purpose of creating music, rest of the sounds are just derivatives of these 12 sounds, or sounds that lie in between them.
--> Home Key/Note
Majority of music (I am pretty sure over 99%) has an affinity to one sound. Could be A, B, or any other non standardized sound. But this is the sound which any particular music wants to resolve to. The sound at which our brains feel the most at ease, and comfortable. And this note (for that particular music) is called thehome note.
Here's a practical example. Click on the notes below to hear them:
In the above given notes, the C note is the home note. Try playing any of the notes randomly. No matter what sequence you play in, your brain would always want to end on this C note. It will always feel the most stable.
Note: Context matters a LOT in music. In the above given notes, C is the home note. But if different notes are selected than the above ones, C might not be the home note.
So when you select a particular home key, you are essentially saying that I want this sound to be the most stable note in this music. Many other sounds will be played as well, but whenever this note is played, your brain will feel the most at home.
This home note is represented by the white bubble in the visualization.
“Alright. But where did major, minor come from?”
Music is the arrangement of sounds in time. So, the arrangement (and also picking the notes to play) part comes from themode. Major, minor, lydian (there are a lot more) are types of modes(also called scales), having their own set of rules to arranging sounds. Different arrangements of sounds evoke different feelings.
Major Mode
Usually bright and happy sounding.
Minor Mode
More melancholic or mysterious sounding. Think of dramatic movie themes.
Lydian Mode
Dreamy and floating feeling. Often used in fantasy or sci-fi music.
“What does adding colours mean?”
If you choose a particular scale, you are already choosing which notes to play (and they are chosen in such a way that they sound well together). But you don't have to always obey the rules of the scale. You can choose other sounds too that don't belong to this scale. Now, they may sound a bit weird at times, and unpleasant. But they add more colour and spice to the music. Makes it interesting and adds a whole different dimension to songs. After all, life isn't always upbeat, happy or unidirectional. There are some weird, haunting, or even unpleasant moments too. And adding these weird notes creates the same effect.
In the above visualization, these out of place notes show up as differently coloured bubbles. (Only when you choose “Yes” for adding more colours. Otherwise they aren't played at all)