Microbit micro: Breadboard MBT0009

Not sure that I have understood this board correctly.  

Does the USB input at the side of the board deliver just power (or power and data) ?

For me, it does not detect as a USB device when plugged into the breadboard.      Which means that I need to plug a USB cable into the top of the breadboard to program it (which of course, also delivers power).   

So I am confused, what is the purpose of the USB connector on the side.      If just power (no data) then it is pretty useless.     

Help.