The front USB A port provides power so you can charge other devices such as a phone or a handheld radio (BCD 436 / SDS 100). The micro USB port does not have a function. I think there were plans originally, but sadly they did not come to pass.
Front Micro Usb is for programming (mass storage) and serial connection.
Front Usb A port only provides power to usb devices.
Front LAN port is for third party connectivity.
Rear Micro Usb port works with third party software. (Bandscope)
Rear RJ-45 port is used for gps module
Port descriptions are extremely vague in the manual.