This document tells a user how to use your system. The format is up to you. Pick your favorite User's Guide and copy its format. You may even want to use the UNIX man page system. Assume that the user knows nothing about your project. Provide an overview and then details of each subsystem. Make sure you explain how the whole system works before delving into the details. This document is for the end-user or another programmer, so you have to explain the obvious, e.g.. Basically, you have to tell someone how to use your system.