The "small" problem was that i took the relay into my hand when i plugged the plug, and it tazed me super hard, like my whole arm shook... I suspect that it came from the solder on the bottom of the card... Can you confirm it
I assume you had it plugged into the power line?
Also, what precautions should i take while handling it
Don't touch anything while it's plugged-in to dangerous voltages! And, mount it in come kind of enclosure so nobody else touches it either.
- How does it works ? Why is there 3 pins (VCC, IN1, GND ) ?
First, you don't just have a relay, you have a relay module, which is a PC board with a relay, a driver circuit, and a couple of LEDs. That's good, you usually need a driver circuit to drive a relay with the Arduino.
[u]Here[/u] is a schematic for a SPDT (single-pole, double-throw) relay without the driver.
There are 5 terminals. Two for the coil, and three contacts. Notice that there is no electrical connection between the coil and the contacts, so if you are switching AC power the AC power is totally isolated from your low-voltage circuitry.
"C" is common and it's connected to "NC" (normally closed contact) when the relay is not energized. When the relay is energized, "NO" (normally open) gets connected to common. NC and NO are never connected together.
How do i plug it to controll it from the arduino ?
Connect VCC to 5V and GND to ground. Connect IN1 to the Arduino output pin of your choice, and program that pin to control the relay.
Since you bought something from an unknown manufacture and a flakey supplier, you don't get a schematic or complete-detailed specs.