There's always a clue, if you just seek it!
Writing is ALWAYS informed by a purpose - as Cicero said, to delight, teach or move - that is, to entertain (comic monologue), explain or educate (a dummy's book), or persuade to action or belief (a sermon, an ad).
YOU have a voice - texts change the world, writing and power - author/ authority. Shelley said that poets are the "unacknowledged legislators of the world."
Websites to help
Rhetoric & Composition Materials
Guide to Understanding the Rhetorical Situation
Using MLA documentation
Writing Annotated Bibliographies
Resources for Annotated Bibliographies