One of the challenges to starting any User Requirement Specification (URS) is to envision a structure which can allow for traceability as the project continues. The attached sample URS is a starting point which is laid out in tabular format to allow easy integration into a Requirements Traceability Matrix (RTM). The URS is separated into logical sections to prompt the writer to consider what requirements are appropriate for their specific implementation an organized way. Requirement examples provided in each section are intended to provide some initial ideas which can be further embellished and added to as appropriate for a project.
This document does not necessarily include all the requirements for your system, but I hope you find this a better starting point than a blank screen!
Download the Microsoft Word version here: