If your staff assume their job is X, and you really want it to be Y, you are setting yourself up for poor performance and staff turnover. If the difference between your perception of their job and theirs' is too far apart, it can result in you giving them a stern lecture just when they are expecting a pat on the head. I'm amazed at the number of managers and owners who expect their staff to be psychic and automatically know what's expected. It doesn't work that way. Every workplace is different, every employer has emphasises on different aspects of their businesses.
Staff have different levels of experience and understanding of their role.
A broad variety of people describe themselves as these things and it's up to you to clarify the roles as they apply to your business. I normally teach business owners and managers do this through the process of orientation and induction training. When a new employee starts, you should devote sufficient time to acquaint them with your business philosophy, the environment they will be working within, and your expectations for their performance and conduct. A job description is a concise statement, in writing, of the major goal and key responsibilities of a particular position. It is usually no more than two pages in length.