Connecting a 12v relay to microcontroller circuit
From the data sheet's wiring diagram, we can figure out the pins. The middle pin is the Common pin. The Top Right pin is the Normally Opened switched pin. The Bottom Right pin is the Normally Closed switched pin. The Top and Bottom pins on the Left are the Relay Coil pins.



The diode would be placed, Cathode to the top pin, Anode to the bottom pin. 12V input would be connected to the top pin, the transistor's Collector to the bottom pin.

To test it out, you would use the multimeter's continuity mode to the common pin and the NO pin. When the relay is turned on (PC0 is High, Transistor is on), there will be continuity across the common and NO pin.