stdio.h is a header file that is a part of the standard C library. It contains a number of routines used for standard input (usually from the keyboard) and output (usually to the console/terminal).
It can be included into your source.
It can be included into your source.
It can be included into your source.
The stdio.h file is used in c programs in order to import declarations of important functions and constants that are useful in doing input/output, using the library facilities of the compiler.
The latter is better.
No. That's a header file used for input and output.
Options/Compiler/Directories/Include - set the path of the include files.
Unity3d, Java, C, C++, C#, there are many programs they could use.
Platform dependent, possibly LIBC.LIB or something like that.
No, use java.
You cannot, but you can use any text-editor to write C sources.
Their name, content and function.