An bibliography is a list of sources used or consulted when writing an essay or research paper on a particular topic. An annotated bibliography simply means each source also contains a brief summary and evaluation of the source.
As you research your topic (Emily Dickinson and "I Could Not Stop for Death"), create a list of sources you believe you will actually cite in your paper. It is easiest to go ahead and create the source citing in whatever format your teacher requires (usually MLA or APA format) for the paper. When you actually begin to compile notes and ideas for the paper from these sources, jot down in 2-3 sentences that briefly describe what the source was about. Then, you in a couple more sentences, you can describe how you used it, how it compared to other sources, and overall, how helpful it was. I usually encourage students to keep an objective voice in the annotated bibliography. This means keeping the source as the subject of the annotation, rather than writing about yourself as the author of the paper. A quick example is to to say: "This source was helpful in..." rather than, "I used this source to..."