Just about all electronics use a UART serial port with RX and TX pins for debugging, bootloading, programming, serial output, etc. But it's rare for a computer to have a serial port anymore. Thus, a serial cable is an essential part of any electrical engineer's toolkit.
This is a USB C to TTL serial cable with an FTDI FT232R usb/serial chip embedded in the head. It has a 6-pin socket at the end with 5V power and ground, as well as RX, TX, RTS and CTS at 3V logic levels. Useful whenever you want to communicate with a TTL serial device such as an Arduino Pro Mini or ESP breakout, and the pinout will match up exactly to any 'FTDI' 6-pin header.
The version we have is the 3.3V Power / 3.3V Logic. The data signals are at 3V and the power line provides 3V as well. We suggest this for any product that needs FTDI cables and draws less than 50mA from the 3V power pin. Because the cable is 5V-logic compliant, you can use it with 3V or 5V logic just fine - no level shifting required!
If you have a device that has 5V logic and requires higher current 5V power, you should check out the FTDI friend.