Datasheet

the chip or crystal of the radio, green/blue is 900MHz & red is 433MHz

Power Pins

GND - this is the common ground for all power and logic

BAT - this is the positive voltage to/from the JST jack for the optional Lipoly battery

USB - this is the positive voltage to/from the micro USB jack if connected

EN - this is the 3.3V regulator's enable pin. It's pulled up, so connect to ground to disable the 3.3V regulator

3V - this is the output from the 3.3V regulator, it can supply 500mA peak

Logic pins