Patterns, not rules
No one hands the system a list of musical rules. It is shown a large collection of existing music and finds the regularities itself: which notes tend to follow which, which chords tend to lead where, how often sections repeat. Generation then means continuing in the style of those regularities.
From a sentence to a track
A request like "a slow, warm guitar loop for a rainy afternoon" gives the system a direction: slow tempo, guitar, mellow mood. It uses that direction to select among the patterns it learned, and returns a short piece that fits. The result is a draft. If the tempo feels wrong, the person asks again or edits it, and the next version is usually closer.
Learning from examples means the system reproduces the tendencies of the music it was shown. That is the source of both its fluency and its limits, and it is the thread that runs through every approach covered later.