J21 is is for 7-15v (actual valid input range might lower/higher, but 7-15v will work) input into the TPS62133 which provides 5v to the rest of the board. The pin closest to the edge of the board (with a square shaped solder pad on the bottom) is Ground.
J1 is for an optional themistor (just shorted together if no thermistor is present) for use when charging a 1 cell lipo battery that is hooked up to J2 (again the pin with the square shaped solder pad on the bottom/underside of the board is Ground).
Hopefully the schematic for the board will be made available soon.