In EPLAN, the logical and graphical data are managed separately. Logical data is stored in the function definitions, graphical data in the symbols. This separation is significant when working with an engineering approach and offers a number of additional advantages for a modern CAE product (such as standards independence).
EPLAN supports both a graphics-oriented drawing interface (copy pages, add macros, place symbols, etc.) as well as a logic-oriented interface based on an engineering approach (working with devices, predefined listed, navigators, "use existing", etc.).
If you work with the graphics-based interface you don't need to worry about functions or function definitions. Function definitions are already assigned to the symbols in the standard symbol libraries. You simply place a symbol or a macro and the default assigned function definitions are automatically added.
If you work with the engineering interface or want to adapt reports, numbering, etc., however, it is necessary to understand the concept of functions.
See also
Function Definitions: Principle
Connection Point Designations and Descriptions