MinGW can compile Ada, C, C++, Fortran and Objective-C. The compiled programs are .exe files; they can use the Microsoft C runtime MSVCRT.DLL and several other Microsoft libraries.
MinGW also provides the import libraries (like libadvapi32.a and libmscvcrt.a) and the header files (like <windows.h> and <stdio.h>). GCC needs these to compile programs that use the Windows API. The compiled programs only need the DLL libraries. Microsoft includes the DLL libraries with Windows.
MinGW always produces 32-bit code for x86. MinGW never produces 16-bit nor 64-bit code.