USB explorer 3.3V power pin

The USB Explorer from Sparkfun seems to be the preferred way to access the xbee pins on a breadboard.
Can you explain how the device can be powered when the USB is NOT plugged in? There is a 5V pin and a 3.3V pin. I would assume that either can be used – but not both. Also, I notice that when the 3.3V pin is used for power, that the LEDs do not function to show tx, rx, power. Is this correct? Would these lights work if I used the 5V pin for input?

Also, can you state how the remaining pins such as RTS, DTR, etc should be set (float, high, low).

As the board you are referring to is manufactured by Spark Fun Electronics, I would strongly recommend asking Spark Fun this question.