Here are some guides for Garageband for iOS
The Apple Support Guides:
For iPad https://support.apple.com/guide/garageband-ipad/welcome/ipados
For iPhone https://support.apple.com/guide/garageband-iphone/welcome/ios
Other helpful sites and videos:
Best order to record tracks:
-Drum Beat
-Bassline
-Harmony
-Melody and/or solo
TuroLessons 