C++ :: How To Use Two Header Files In Program

I want to use two header files in my program. Here is exactly what I want to do.

-In the first header I have a binary tree and a structure.
-In the second file I have another functions that need to use the structure in the first header.
-I also want to use a function from the second header in the first.
-And finally I want to do actions with both headers in a "main.cpp" file that contains only int main() function.

How to include the headers in each other and in the main.cpp to be able to do the actions above?

I try to include the first header in the second one and the second one in the first header. Then I include both headers in the main.cpp file. But the compiler shows me many errors.