cpp problems:instantiating class?

hello, i used microsoft visual studio 2019 community c++ compiler ide to build a simple demo project, in declare class with header Calculator.h and class implementation code Calculator.cpp

class Calculator

{

public:

int Add(int a,int b){ return a+b;}

long Multiply(int a, int b{return a*b;}

}

but when i try to instantiate and use the code, the intellisense do not sense there is the Calculator class exist, and i write statement using Calculator,it indicate me no such class exist, what are the problems and how to fix them

}