Writing about any subject engages many modes or ways of thinking.
Look at the two pictures above. Describe specific details you see in each picture.
You have just experienced some thought processes used in writing.
Writing starts with observation, with the writer noticing and choosing something to write about.
Writing often involves description, with the writer using concrete details.
Writing generally involves explaining, perhaps explaining "why."
Writing may involve inference on the basis of evidence, interpretation on the basis of observation.
Writing often involves synthesis, or finding the common link between things and explaining that link.
Writing involves selection and focus. The writer may focus on one main approach or idea in one piece of writing. For example, one writer may compare the meanings of the two images above, while another may contrast the feelings they evoke, describe similarities in subject matter or argue for his or her interpretation of the paintings.
Writers consciously or subconsciously choose the type of thinking to focus on in their writing.
Writing can be thought of as thinking made visible; it helps bring into consciousness normal human thought processes. Just as your thinking about the pictures was unique, your writing will be unique, as there is no one, single way to think about a subject; there is only the individual writer’s way. And the writer's way of observing, thinking, recording and structuring writing may change from situation to situation.
Writing also doesn't happen all at once, but as a process, just as you went back and forth between looking at the pictures and formulating your thoughts. Writing clarifies and presents the results of the writer’s thinking process. (A definition of "process" might be useful here: "a system of operations in the production of something; ongoing movement." (“American Heritage Dictionary”))
So, to recap, writing:
Academic writing often is expository writing, or writing that explains. As you write for college, you may explain a number of things, such as observations, feelings, experiences, your own and others' thoughts. You're usually expected to offer your own insights into a subject, often using a method of investigation and explanation used by a particular field of study.