header file

how do i make a header file..?

In the narrow sense, you use a text editor - they're just text files.

If you want to know how to divide things up into source and header files, there's a FAQ
FAQ > Multiple source files for one program (C++ example) - Cprogramming.com

Yes, it's C++, but the basic rule of declarations go in .h files and implementation goes in .c files still applies.