This is a dev board for advanced developers, who need in-circuit debug. It is based on ST-Link V3 Mini and differs only in form factor and ease of connection. Some unused ST-Link and Flipper Zero pins are broken out additionally.
You can update the firmware, develop and upload your own firmware to Flipper Zero via USB without this dev board! It is only needed for in-circuit debug while the firmware is running using GDB/OpenOCD/etc. If you don't know exactly how to use it, you don't need this board.