Relay Voltage Rating Question
That particular relay is a dual coil latching relay.  You would apply a short pulse  of 12 V to one coil to set the contacts in one position, and a similar pulse to the second coil to set the contacts to the other position.

Under "contact rating", the datasheet states that the contacts are rated to carry 2 amps - I don't know where the 5 Amp rating in the feature list comes from...

For normal (non-latching) relays, you apply power to move the contacts to the "normally open" position, and remove power to allow the contacts to return to the "normally closed" position.