Most student writing is in response to a brief or a question, usually given by a lecturer. Thinking about this brief or question will help you decide the purpose of your writing. Tasks 1 and 2 will give you practice doing this.
In addition, a sentence or two about the specific purpose of the assignment is often found in the introduction section, or in the first paragraph. In Tasks 3–4 you will do exercises connected with identifying the purposes of some assignments by looking at the questions and the reasons the writers give for answering the questions.
The assignment questions and extracts in these tasks are taken from real coursework written at British universities so they give you an idea of the kinds of tasks to expect.