Marshall CODE 50 as a practice rig

I want to use my CODE 50 as a practice rig, but am not sure of the best way to play music through the amp so that my headphones play a mix of music from my iPhone/iPad/MacBook Pro + my guitar.

Do I use the USB port?

Do I use the mini jack port for devices?

And for both, what cord do I need to get from Apple’s USB-C output to the amp?

I’m overwhelmed by the configuration options and figured you guys have done this and could simplify it.