My God I even had a comp science teacher ask me this.Arrrg one will go mad.
It's simple.Cut a few funtions out of you code and paste them in a file with a .h extension and call #include "your_header_name.h" to include that.
Note: not < > but " " if it's in the current directory else you have to supply the full or relative path.
All the rules are same as normal C++ syntax.
That was very simple thing.Headers can be used for more things.They can just contain funtions declarations without definitions.In that case it will be used to link to a static library.
Eg.Make a header file with 2 funtion declarations like fun1(); fun2(); only
Include it with a cpp file and call the funtions and compile.
You will get no errors on compile but on linking you will see an error similar to the following:
undefined module fun1() refferenced from Module main.cpp
undefined module fun2() refferenced from Module main.cpp
I hope you understand a header in not really diffrent from a cpp file.Btw you can also include .cpp files.
write some functions||define some macros||define structures/classes etc...
DO NOT include a main() function
save it with the name you want
you use it through: #include "..."
if you have variables in your header, do not redeclare them in your programs or it will give you an error "Multiple declaration for variable..."