What are the pins for in this Relay module?
Typical relay module clone, they are all similar. Below schematic is per channel.
Keep in mind that RY-VCC (JD-VCC in the schematic) is for the Relay section, while VCC on the 4 pin connector is for the opto-isolated side.
https://arduinoinfo.mywikis.net/wiki/ArduinoPower for a full wiki on using these.
See passerby his answer for the whole schematic of your module per channel. For the data sheet of just the relay check sbell's answer. However, to activate it you should provide the VCC with +5V. The GND connected to the GND and give a +5V signal to the IN1 or IN2 to activate it. IN1 and IN2 should be connected to one of your output pins, they will be able to switch your relay. But when I look at the schematic passerby send you it might also be possible that you'll have to put your output pin to LOW in order to activate it.
I just wired up one of these modules a few minutes ago to confirm the info I'm posting below.
From your controller (eg Arduino or Raspberry Pi) connect Ground (0V) to the relay module's GND and Power to the module's Vcc. In most Arduinos the power will be 5V, in a Raspberry Pi it will be 3.3V - but these relay modules will work OK with 3.3V even though they are officially rated at 5V. Connect one of your I/O pins (in output mode) to IN1 and the value on that I/O pin will control Relay #1. Connect a second I/O pin to IN2 to control Relay #2.
These modules have the circuitry described above built-in so you don't need to add it - that's only needed if you are driving a stand-alone relay directly. All that's usually needed is a few Dupont jumper wires.
The other three pins (GND/Vcc/JD-Vcc on a separate connector) are normally not used and the jumper is left in place. They are used to power the relay switching and pick up the Vcc and Gnd off the data connector. By removing the jumper you can power that other Vcc pin separately.
If you need to do this or need the optical isolation feature to keep high voltages away from your controller, you need more expert advice than we are giving here; in fact if you don't already know what to do then you shouldn't be doing it as there is a good chance of damaging both people and devices.