When you are explaining what is meant by context, audience, or purpose; or you are describing the writing situation for an essay, it is useful to engage students by asking questions that encourage them to reflect on their own knowledge. For example, when introducing audience as a rhetorical concept, you might ask, "Who did you think of as your audience when you completed your assignment for today? How did you make choices based on that audience?"
At some point though, students will begin to ask specific questions. This is an excellent time to define the concept you're introducing and provide them with clear answers.