I guess there are two sides of music to learn on the Amiga. I am a noob at music, in the sense of I can play a triangle and sing and er, that's it really.
You have the performance side, where you are playing an instrument, or wiggling, wobbling, pitch shifting or whatever, a noise in real time. Scratching is pretty easy to pick up, when you understand the technique used on a vinyl deck.
The other side is musical arrangement, where you can drag together different instruments and "performances" as it were. Drums are way different to vocals. Double bass is treated a bit different to a rhythm guitar, although the two are closer than the previous pair.
The rest is like any other art. It's down to refinement, technique, talent. I will never be a pianist of any description. I know real pianists, it's very humbling.
Be aware that 99.99% of all musicians never earn a living from their fun.

You got two kinds of instruments, a sample that can be manipulated like an instrument (IFF8 and similar, 8SVX) and they are very limited to their musical range in octaves (with most software and Amigas).
Then you've got longer samples, things like drum loops, vocals, orchestral crash, that kind of thing. You can speed it up or slow it down to start with, but you are kind of stuck with a few speeds unless you have a different replay speed and sample rate.
That's where I stop with Octamed really. Those are the simple basics, and they cover DMCS as well.
It's wise to play around with Trackers as well, if only to see how existing song mods are made. Don't limit yourself to one particular program, but do be very careful how you extract samples and preserve them. Make sure you power off before reading an alien .adf download.
It's not wise to try out an Amiga demo, like the music, and rip the content and reuse it. Better to just stick with downloadable mods than go hunting for that one sample. It's a near certainty, you can get it better elsewhere. If you know what song and artist performed it on CD or Vinyl (with a nod that a sample is just that, a short piece, not a substantial part of the whole track).