1. Stand so the red X is in front of you. 2. Make sure to stand exactly as it is shown in the attachment below. 3. Dig down. If you don't see the chest, dig.
Search for visible deposits of iron. When there isn't any more, look for coal. I found from experience that iron is almost always 2-3 blocks away from coal. So.
A monster spawner can be obtained in Creative mode by taking it from Creative inventory, by using the /give command, or by using pick block. It is initially.