non-managerial employees are responsible only for themselves and their work. managers are responsible for the productivity of others.
a common mistake of “non-managerial employees” is to comment (or complain) about the work ethic of another “non-managerial employee” who isn’t performing the way they think they should. they may even complain to their manager about this. but that is a huge mistake, because *it is not their responsibility * to evaluate the work of other employees, and they will likely be told as much.
a less common counter-example is when a manager defaults on their responsibility and tells a non-managerial employee to report on the performance of another employee. again, totally inappropriate.
Almost too broad a question to be worth answering and you could write many books on the topic. But in short managers are expected to:
Think, analyze, plan, hire, fire, improve productivity, budget, motivate and be accountable for results (not activities).
Individual contributors do few, if any of these things. Of course, some professionals are required to do some of these things too as their main job. i.e. accountants budget and plan money. Architects design and plan projects and budgets.