The Visual Basic 6 SDK is provided to support legacy applications and add-on tools. New development in Visual Basic should use a Basic language which supports ActiveX/COM, for example VB.NET or VBScript, or which can build standard DLLs. The old-style Visual Basic EXE as an add-on tool to Visual CADD is not recommended but is still possible with proper configuration of Visual CADD.
The \Source\ folder contains the Visual CADD API declarations in BAS files. They should be copied to your project folder for inclusion in your Basic projects.