Writing a summary of a poem is not necessarily an analysis. A summary is a way in which you show that you understand the main idea(s) and what basically is going on. First, look at the title of the poem for insight into the main idea. Second, read the whole poem to get a feel for what is being discussed. Next, determine who the speaker of the poem is. Many times the speaker of the poem isn't the author but a character that the author has created. If you still can't follow what is going on in the poem, search for clues within the symbols and imagery presented. Remember that symbols are word-pictures that stand for something more than themselves and imagery are ideas presented through the five senses (sight, smell, sound, touch, and taste).
Write down a few of the symbols and images that you understand clearly and focus on them to help you to understand the poem as a whole. Draw some conclusions and start writing your explanation.
TIP: double-check the assignment requirements. If your teacher just wants a paragraph, then you could mention the main idea and a few examples of imagery from the poem briefly. If your teacher wants a one page summary, though, you might want to consider discussing three examples from the text in a paragraph of their own.
Good Luck! :)