How do you build a system? It is just like designing a house. You do not go out there and mix cement right away. First, you sit down and think how you would like your house to be. Then you get a pencil and start drawing.
The same thing goes in software development. You "draw" the functional specifications that make up your system and then "draw" the details of process specifications that goes with each function.
For a detailed discussion, please visit: Getting Started in Software Development.