Now that you have your poem picked, and the vocabulary to talk about it, it's time to write!
Why does writing about poetry matter? Well, it makes us look more closely at a poem than is possible just reading it. To make an argument about a poem, you need to pick it apart and zero in on tiny details. In going through this process, we can come to appreciate what makes a particular poem tick-- which could make us better poets, or at least just better appreciators of poetry.