Sound is vibration in the air. Music organizes that vibration in four main ways. (Our worlds are silent for now, but these are the ideas we would use to add sound.)
Pitch. Pitch is how high or low a note is, set by how fast the air vibrates. The note A used for tuning vibrates 440 times per second. Notes whose speeds form simple ratios, like 3 to 2, sound good together.
Rhythm. Rhythm is how sounds are placed in time. A steady beat in groups of four feels like walking; groups of three feel like swaying. Playing slightly ahead of or behind the beat makes music feel human instead of mechanical.
Harmony. Harmony is two or more notes played together. Some combinations feel settled, others feel tense. Music moves between tension and release, and that movement is a big part of how it creates feeling.
Timbre. Timbre is the character of a sound, the reason a flute and a trumpet sound different on the same note. It is what we would design first for our worlds: soft sand for Desert World, slow waves for Ocean World.
Try it: hum one note, then slide it up and back down. That small change in pitch already carries emotion.