You really should compile LinkedList.h by itself to be sure that you've at least corrected all of its syntax errors before trying to use it together with other (unproven) code.
I think I remember you saying that you're using g++. If so, you can call it with
g++ -c LinkedList.h
The -c option means it will just compile that code and not try to link it, so it will work even though there's no main function.
Alternatively, of course, you can write a trivial main function that does nothing but instantiate a LinkedList, and compile in the normal manner.