The i2C-6ULX-B has a Micro USB OTG interface. It's default on Host mode.
You can use Micro USB to USB Type A convert adapter, then connect the USB flash disk into it. The board will auto find and mount the flash disk. The linux support FAT32, EXT4 filesystem with USB flash disk.
In Device mode, the i2C-6ULX-B will as slave device connect with other USB host port.
Below is simulate a RAM device as storage device on the USB host port.