Here is the most generous trick in music: take the seven notes of one major scale, change nothing, and just start from a different note. You get a completely different mood. These are the modes · seven moods hiding inside every key you find on this site.
Happy, bright, home. Most pop and folk lives here. "Let It Be" is pure Ionian comfort.
Start from the 2nd note. It is minor, but with one raised note that adds a jazzy, hopeful shimmer. Miles Davis built "So What" on it; "Scarborough Fair" and Santana's "Oye Como Va" breathe it.
Start from the 3rd note and the very first step is a half step · instantly dark, instantly Spanish. Flamenco lives here, and metal guitarists love it for riffs that feel dangerous.
Start from the 4th note. One raised note makes everything float, like a film about flying. The Simpsons theme is the textbook Lydian melody.
Start from the 5th note. It is major, but the softened 7th makes it bluesy and easy-going. "Sweet Home Alabama" and The Beatles' "Norwegian Wood" ride on it.
Start from the 6th note. This is the sad one, the emotional one. "Losing My Religion" stays in it from the first bar to the last.
Start from the 7th note and even the home chord is unstable (diminished). Music history almost never uses it · which tells you something: our ears vote, and Locrian keeps losing the election. It survives as spice, not as a home.
Practical use: find your key on the detector page, then click through the seven modes and listen to how the same notes change costume. Improvise in Dorian one day, Mixolydian the next · same fingers, new feelings.