Just looking at the photos I'd say connect any four digital OPs to IN1-4.
Connect the Arduino GND to the GND on the board.
What's not clear though is what VCC means in this context, a board like this shouldn't heed VCC from the Arduino (unless it's for the LEDs, or maybe the relay coils are 5v), and where does the 24v come from. There are two GND/VCC terminals, is one of them for 24v?
I would ask the suppliers for more details, a wiring diagram or a schematic.
Alternatively tell us the relay details (printed on the top) and trace where the GND/VCC signals go and tell us.
Rob