We don't know how your project is set up, but probably not like that. Put your .h file in the same directory as your source file and include it like this: #include "Stack.h". If you want it in a subdirectory for some reason, use #include "mysubdirectory/Stack.h". The brackets (<>) are used for files which are to be found on the include path you have specified in your settings.
FURTHERMORE: if you haven't read the "Before you make a query" thread, please do that now. I don't want to say your subject title is stupid, but I'm strongly tempted to. How is the next visitor going to search for technical information if all the subjects say "Pls Help"?? I'm also of the opinion that a person who types 'pls' instead of 'please' belongs in a chat room instead of a programming forum, because programming requires accuracy and correct syntax.