A song can begin with one idea, a melody, a beat, a lyric and sound.
Then the process starts.
Someone records it, someone produces it, parts get changed, sounds get removed, new ones get added. Vocals might be recorded again and again.
Then comes mixing, then mastering.
And sometimes, after all that work, the artist decides something still isn't right. So they start changing it again.
That's why the three-minute song you hear can represent days, weeks or months of work. The finished track sounds simple.
Getting there rarely is.