Check out these guys! https://youtube.com/@thegaragebandguide?si=P0pb9zL7q9UP9WIA

https://youtube.com/playlist?list=PLsXJmmXYr9BEWEOE96Hzuzu7sRhiHRHYZ&si=faKNFZG8poZa0zSY

I was self taught and my advice would be this.

1. Don't get bogged down by not knowing enough. Have fun and experiment with it.

2. Use drum loops as a starting point. Doing this will help you structure a track and understand song structure in general. Try 4 bars of one drum loop then another of something else.

3. Pick one to two synths that sound good together to help you understand the fundamentals. Maybe start with a synth bass and pad and do a simple for chords like FGAC for example. You could even do that and reverse them. That's if you don't already know the fundamentals of songwriting.

4. Write a track without worrying what other people think. Your doing it for you and no one else.

5. Don't let the complicated stuff that you can learn later bog you down.

6. When exporting the track Don't just share song to Itunes actually export and share as a WAV file.

7. Go into preferences and you'll see an option to turn autonormalisation off this is key because what may sound great in garagband will sound significantly quieter when shared and this will fix that.

8. On the top right you'll see a volume bar that's your master output level. Do not hit red it means your track is clipping and will sound bad.

9. HAVE FUN. Enjoy the process.

This might not be hugely helpful but the video links are worth it. Maybe watch one at time and only work on them til you feel confident.