Connect the Dual Sided 2-in-1 USB-C Charger to a USB-C power source. For the best charging speed, use a USB-C wall adapter rated at 20W or higher, or a Thunderbolt or computer port. It works when powered from an iPhone, including the iPhone 15 Pro Max, but iPhone power limits it to about 1W, so use a wall adapter or computer port for full speed. No software or app is required; just plug in and charge.