The functional description is a rough description of the functions you'll need to design your product. The functional descriptions should be entered as documents in Document Management and connected to the function structure in PDM Configuration at a later stage.
Functions can be assigned on top of the product structure. This enables different disciplines/departments to create their own views of the product. The functions can be organized hierarchically.
The sort of information you use to describe the functions is entirely up to you and is dependent on what the functions do. The document could consist of a list of the function names and a short description of what they do. Later on, you will describe these functions more thoroughly.