Arguments are everywhere
You may be surprised to hear that the word "argument" does not have to be written anywhere in your assignment for it to be an important part of your task. In fact, making an argument—expressing a point of view on a subject and supporting it with evidence—is often the aim of academic writing. Your instructors may assume that you know this and thus may not explain the importance of arguments in class.
Most material you learn in college is or has been debated by someone, somewhere, at some time. Even when the material you read or hear is presented as simple "fact," it may actually be one person's interpretation of a set of information. Instructors may call on you to examine that interpretation and defend it, refute it, or offer some new view of your own. In writing assignments, you will almost always need to do more than just summarize information that you have gathered or regurgitate facts that have been discussed in class. You will need to develop a point of view on or interpretation of that material and provide evidence for your position.