See Tips on Posting Good Questions, especially the first item about searching. One of the results obtained by searching for stdafx is Precompiled Header Files. which should help you to get a better idea of where to look and what questions to ask if that does not answer the question.
The contenst of the stdafx.h file depends on the project. Each instance is generated or created for the project. You must obtain it from the project that you got the other project file(s) from.
Explore other projects that you have generated and that have been generated by ohters. Explore the samples provided with VC. You can learn very well what those silly stdafx files are. The name stdafx results from MFC but the name seems to now be an essential standard that VC uses for most all projects.