Most likely, looking at the very blurry picture, the three terminals on the right, from top-to-bottom are "coil 1", "COM", "coil 2", while the other two on the left are "NO" and "NC" contacts (from "COM"). This is how most SPDT relays are set up, with the common center pole between the two coil connections. Use a multimeter set to 1K ohm or lower range, and check the connections; the coil will register with a resistance, whereas everything else will either be infinite resistance (open/no continuity) or zero resistance (closed/shorted). If those two aren't the coil, then they'll be the contacts on either side of "COM", and the other two on the left will be the coil.
To hook it up to the Arduino, see here:
Just use a 6 VDC supply across the coil to energize the relay; make sure your ground is connected with the Arduino's ground. DO NOT leave out the resistor -OR- the diode, they are important!