Am I required, as a small business owner to give a job description to new hires?

[Moneypenny]

I am new to all of this. I need to know if there is any legal obligation to give my employees job descriptions. I'd rather just have them "open" to do any task I need done. I want each employee to act as I would, as everything in the office is important, it all needs attention. So, do I really need to give them a description of what they will and will not do?