A few of the language choices a writer makes will be actively contributing in important ways to the style the writer needs to create to suit their writing to a particular audience and purpose. You will gain good marks if you discuss these important language features.
When you are asked to comment on language choices, therefore, your teacher expects you to discuss the effects of interesting and effective aspects of language that a writer has made. To do this well, you also need to discuss two things: i) where applicable, the method the writer has used (this might be, for example, a use of vivid simile or metaphor, hyperbole, personification, onomatopoeia, and so on) and ii) the purpose intended behind creating the language effect.
It's important to realise just how many marks this kind of analysis creates. Never leave discussion on language wanting. For example, did you realise there are often two purposes you can discuss behind each quotation you use? There will be a purpose at the point the quotation occurs within the text, but there will also be a secondary purpose you can discuss - in literary texts, the quotation will also be contributing in some small way to the overall themes of the writing.