With questions like this one, the answer should include your exploration of various devices such as simile, metaphor, alliteration, repetition, diction (word choice), etc. Does the poet use a lot of figurative language, or is it very literal? Are there any parts of the poem where the poet uses words that all have the same connotations, such as a stanza filled with words like "dark, dank, gloomy, and black"? Is there a word, phrase, or image, that is brought up more than once?
After you've gone through the poem and found these different devices, and discovered the poet's particular approach to language, the second part of the question becomes easier to answer. What is the poet's particular language contributing to the over all message of the poem? Using the example I gave before, a stanza filled with words like "dark, dank, gloomy, and black" would create a melancholy tone. If the over all message of the poem is that the world is a dark and sad place, that would be a use of language that would be significant, so I would include it in my answer to this question. If the language used in a poem is all very literal, and the message of the poem is about the rigidity of society, you could argue that the lack of figurative language is a way for the poet to evoke that feeling of restraint. Essentially, the question is asking you to find ways that the poet has used the words of the poem itself to influence the over all effect of the poem.