This screen (at the end of the process of creating a new mpi project with CDT / PTP) warns of the error you are describing and says that you should go to the next screen to easily add the mpi header to your project.

I'm not sure what you mean by "explain the reasons for the debug / release folder." If you just mean that you never use the Eclipse build command, that's fine, but Eclipse is built to have many features; some people use them all, and some people hardly use them.
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