How is power and communication from USB achieved at the same time?
One easy way to provide power and communicate with the device at the same time would be to use one of the FTDI USB TTL Serial Cables. Make sure to pick a 3.3V device and as that device doesn't draw much current the TTL-232RG-VSW3V3-WE with an output of 3.3V at up to 50mA would be suitable. 

The Wiki page for the product shows the minimum pin connections when using the serial interface in the first application circuit. Just much those up with the corresponding pin numbers / colours from the FTDI datasheet.

Once the FTDI drivers have been installed (if required you may already have them) you'll just require a terminal emulator to talk to the com port. I quite like RealTerm as it has a nice set of features useful when debugging embedded systems.