New to C programming are we? You need to learn how C program files use headers to describe/define structures and interfaces. This is basic computer science and programming 101. For example, if I have a C source file that implements some API (functions) that other programs may use, I will create a header file that specifies the signature of the functions (API) so other applications can use them. Example:
In this case I am defining a structure and making it a proper type (mytype_t), and then I am declaring that my code includes the function myfunction(...), in a manner that other programs can use it if they link to my code.
If you don't understand all of what I am saying here, you have some serious studying to do... :-)