"High" and "Low" are not universally agreed upon, so I'll be a bit vague. The highest level might be pure business, describing business processes without even mentioning computer systems. The lowest would might be technical API designs. In the middle somewhere my team tries to write them to describe user interaction with a particular system, but free of any user interface language like buttons, pages, list boxes, double click. We write a separate doc with those UI details.
I recommend Alistair Cockburn's Writing Effective Use Cases book to nearly everyone. He shows a wide variety of styles and levels for different audiences. Something in there is likely to look like what you need. BTW: Instead of high and low he uses cloud, kite, wave (sea-level), fish and clam.