In this poem Poe imagines the sounds of four different kinds of bells, and the times and places where you might hear them. There's no plot in this poem, exactly, but there is something like an emotional arc, as we move from light, bubbly happiness to sadness, fear, and misery.
First, we hear silver bells on a sleigh, and the speaker tells us about the happy, tinkling sound they make. Next we hear the golden bells of a wedding, and he describes their mellow, joyful noise. Then things take a turn, as we hear the sound of brass alarm bells warning us about a fire. Finally, we hear the heavy, miserable sounds of iron bells. The sound of those bells makes the people who hear them really sad. Apparently, however, the creatures that are ringing the bells (the "ghouls") are delighted by the sound and the misery they are creating. It's classic Poe – things really come to life as soon as the terrifying noises and the weird monsters show up.