This is a bit of a niche video, but it is suitable for new musicians and those who want to find tools to better take advantage of their mobile devices.
Apple's GarageBand is the first app you'll want to delve into if you're new to making music on the iPhone, as it's loaded with different instruments for you to experiment with.
Music Memos, an app that's always gone under the radar, is super useful for recording song lyrics or making notes on your compositions. There's a one-tap record button so it's easy to get started, and Music Memos will record the exact notes you're playing so you can come back to your work in the future.
For actually recording high-quality audio that's similar to what you'd get in a studio, the iPhone's microphone just isn't good enough. You're going to want an accessory like iZotope's Spire Studio, which is basically a miniature recording studio that can go anywhere. It's not cheap at $349, but it can capture great sound.
There are tons of other apps and tools out there, so if you're a musician who records with an iPhone or iPad, make sure to let us know which accessories and apps you prefer to use in the comments.