Now that you've assembled your data about the application, it's time to write up a specification. Software specifications can range from very formal, contractual documents that include time estimates and deadlines, to a simple set of descriptions of what the programmer intends to build. The purpose of the specification is to give everyone involved in the project a point of reference for what the developer will create. It spells out the problem to be solved, the functionality required, and the scope of what the program should and shouldn't do.
Your scenario is rather informal and your application is simple, so you do not need a detailed formal specification in this case. However, a basic write-up of what you know will make sure that you, your boss, and the users are all on the same page.