The USB-C to USB Adapter connects a Mac that has a Thunderbolt 3 (USB-C) or USB-C port to a device that uses a USB-A cable.
To connect an iPhone or iPad with USB-C connector to the USB-A port on a Mac, use a third-party cable such as the Belkin BOOST↑Charge Pro Flex USB-A to USB-C Cable.
Data transfer and charging other devices
Use the USB-A port of this adapter with flash drives, cameras, USB hubs, and other devices that connect to USB-A for data transfer or charging. It supports data-transfer speeds up to 5Gbps (USB 3.1 Gen 1).
For example, you can connect the Apple Lightning to USB Cable to this port to sync and charge your iPhone, iPad, or iPod. Or use the Apple USB-C to Lightning cable to connect your iOS device without an adapter.
This adapter requires no power to operate, but devices that you plug into it might draw power from your Mac. To connect to USB-A devices and charge your MacBook at the same time, you can use the Apple USB-C Digital AV Multiport Adapter or Apple USB-C VGA Multiport Adapter, which also provides a USB-C port for charging.