Difference between using .ipp extension and .cpp extension files

Difference between using .ipp extension and .cpp extension files

Suppose I have 2 header files, 1 .ipp extension file and a main.cpp file:
First header file(like interface in Java):
template<class T>
class myClass1{
public:
virtual int size() = 0;
};
second header file:
#include "myClass1.h"
template<class T>
class myClass2 : public myClass1<T>
public:
{
virtual int size();
private:
int numItems;
};
#include "myClass2.ipp"
And then is my myClass2.ipp file:
template <class T>
int myClass2<T>::size()
{
return numItems;
}
Last one is my main:
#include "myclass2.h"
void tester()
{
myClass2<int> ForTesting;
if(ForTesting.size() == 0)
{
//......
}
else
{
//.....
}
}
int main(){
tester();
return 0;
}
myClass1, myClass2 and myClass2.ipp belong to header file. main.cpp in
source file. What's the advantages by using this way to implement your
program instead of using just .h and .cpp files? And what is .ipp
extension file? The difference between .ipp and .cpp?