Here are the classes, structs, unions and interfaces with brief descriptions:

C_RFC_ATTRIBUTES	Structure returned by RfcGetConnectionAttributes() giving some information about the partner system on the other side of this RFC connection
C_RFC_AUTHENTICATION_HANDLE	Handle to an authentication object which gives access to relevant authentication data received from the client
C_RFC_CERTIFICATE_DATA	Compact structure containing relevant information about the x509 certificate provided by the RFC client
C_RFC_CLASS_ATTRIBUTE_DESC	Structure for reading (RfcGetParameterDescByIndex() or RfcGetParameterDescByName()) or defining (RfcAddParameter()) the properties of a parameter in a function module
C_RFC_CLASS_DESC_HANDLE	Handle to a cached metadata description of a class
C_RFC_CONNECTION_HANDLE	Handle to an RFC connection (client connection or server connection)
C_RFC_CONNECTION_PARAMETER	Structure used for connecting to a backend system via RfcOpenConnection() or RfcRegisterServer()
C_RFC_ERROR_INFO	Used in all functions of the NW RFC library to return detailed information about an error that has just occurred
C_RFC_EXCEPTION_DESC	Structure for reading (RfcGetExceptionDescByIndex() or RfcGetExceptionDescByName()) or defining (RfcAddException()) the properties of an exception key in a function module
C_RFC_FIELD_DESC	Structure for reading (RfcGetFieldDescByIndex() or RfcGetFieldDescByName()) or defining (RfcAddTypeField()) the properties of a field in a structure/table
C_RFC_FUNCTION_DESC_HANDLE	Handle to a cached metadata description of a function module
C_RFC_METADATA_QUERY_RESULT_ENTRY	Structure containing the error that occurred during the metadata query
C_RFC_PARAMETER_DESC	Structure for reading (RfcGetParameterDescByIndex() or RfcGetParameterDescByName()) or defining (RfcAddParameter()) the properties of a parameter in a function module
C_RFC_SECURITY_ATTRIBUTES	Structure passed to the RFC_SERVER_AUTHORIZATION_HANDLER giving some security related information about the calling ABAP partner of an incoming RFC call
C_RFC_SERVER_ATTRIBUTES	Information about an RFC Server returned by RfcGetServerAttributes()
C_RFC_SERVER_CONTEXT	Used in RfcGetServerContext() for obtaining more information about the current incoming function call
C_RFC_SERVER_HANDLE	Handle to an automated ("multi-count") RFC Server, which can manage multiple parallel listening server sessions
C_RFC_SERVER_MONITOR_DATA	Allows to retrieve monitoring information about all busy or idle connections of an automated RFC Server via RfcGetServerConnectionMonitorData()
C_RFC_SESSION_CHANGE	Notifies an RFC Server that a stateful user session has just been created or destroyed
C_RFC_STATE_CHANGE	Notifies the application that an RFC Server changed its state (e.g
C_RFC_THROUGHPUT_HANDLE	Handle to a throughput object which can monitor performance relevant data of connections and servers
C_RFC_TRANSACTION_HANDLE	Handle to a data container for a tRFC/qRFC LUW
C_RFC_TYPE_DESC_HANDLE	Handle to a cached metadata description of a structure or table type
C_RFC_UNIT_ATTRIBUTES	If the external program is the sender of the bgRFC unit, this structure is used to set a bunch of special attributes that determine, how a bgRFC Unit will be processed in the backend
C_RFC_UNIT_HANDLE	Handle to a data container for a bgRFC LUW
C_RFC_UNIT_IDENTIFIER	For convenience combines a unit's ID and its type
CRFC_ABAP_OBJECT_HANDLE	Handle to a data container for an ABAP object instance
CRFC_DATA_CONTAINER	Handle to a general data container (structure, table or function module)
CRFC_FUNCTION_HANDLE	Handle to a data container for a function module
CRFC_STRUCTURE_HANDLE	Handle to a data container for a structure
CRFC_TABLE_HANDLE	Handle to a data container for a table