Metadata and Data Container Classes 
The basic concepts that you need to be familiar with for both RFC client programming as well as RFC server programming, are the metadata classes and the data container classes.
Note
Metadata classes are descriptions of a function module’s importing, exporting, changing and tables parameters and descriptions of the field layout of structures and tables used in function modules. Data container classes specify objects with the correct data layout of a certain function module, structure or table, into which you can fill your input data or from which you can read the function module’s output data.
In most cases you don’t need to work with the metadata classes yourself: the .NET Connector runtime will use them internally and will already give you the corresponding data container classes to work with. You only need to tell the .NET Connector, where to get the metadata information from.