I bought a relay, but I don't know how to hook it up. it's a 30A relay..
i'm a littlebit confuse the relay have 5 pins but in the diagram it's only says 4 Lead Relay.
The label in your second photo that says "NC" (which means "not connected) is incorrect, because it's actually another connection to "Pole". You can leave it hanging - but remember it will be connected to the bulb in your circuit, or you can connect it to "pole", or you can use it instead of "pole" if it makes the wiring easier.
Yes, the coil connections, A and B are where you connect the 12V - they can be either way round with regards to + and -.