You have posted in the wrong forum and I have moved the thread to the correct forum. Normally in header file the function / Class definitions exist and in lib files the implementation of the functions reside.
Depth about it can be explained with an example. Lets we define a Class A in file a.h and its function definition lies in a.cpp Then when you compile and create the library the definition of function lies in the .h files and the implementation lies in the lib files. Like say iostream.h files hold the function signatures of the function and the corresponding lib files has the actual implementation of the function.