In order to write your paragraph on the symbolism in Poe's "The Masque of the Red Death", you must identify the symbolism that exists in the story. In order to identify symbolism you must look at the objects that are focused on by the author and analyze how the author uses these to make a deeper point.
Many symbols exist in this story. Some of them are things like the castle itself. The castle is used by the wealthy as a stronghold to hide from the disease that infects the land. The castle therefore symbolizes their wealth. They hide behind this status to ensure their safety.
Another major symbol in this story is the black clock. The characters react to the clock by stopping everything they are doing. The orchestra stops playing and "the waltzers perforce ceased their evolutions . . . it was observed that the giddiest grew pale". This is because the clock is an instrument of time and thus symbolizes mortality. The characters hear the chimes of this clock and are reminded of how, no matter where they hide, they will all eventually die.
The symbolism continues with the use of costumes and the colored rooms, especially that of the red and black room that no one dared to enter.