In fact the nmake is program for automation of program compilation. It is part of (I think) every C compiler. Here it has debug info turned on (in the makefile), so when you debug it, you'll see to which lines the code belongs to. Also you need the exe to be run in the directory where sources are located. This means that this can be done only with programs, that you have with full source code. But this situation is quite rare in reality
The benefit is that you'll learn the basics.

To compile it, you have to load environment variables for your compiler, then run nmake with the right parameters (nmake /f makefile).
Good luck,
least