can a class be the store container of the another class

[jolley]

i have met such a code:

#include<iostream>
#include<list>
 class intEntry
{public:
     intEntry(int a,int b);
     int add();
     
 private:
     int addition1;
     int addition2;
   
};

intEntry::intEntry(int a,int b)
{
     addition1=a;
     addition2=b;
}
  
int intEntry::add()
{
    return a+b;
}

list<intEntry> &   loadIntoTheList(list<intEntry>&p)
{
    for(int i=0;i<10;i++)
    p.insert(intEntry(i,i+1)) ;  
}

i am wondering the exact use of the "list<intEntry>" and also
i get something similar in the hash containers
see the function object

 
class functionObject
{
   returnType operator()(argement)
{....return returnValue;}
}

since it is the first time that i use it in my practice ,i cannot be sure about the full use of this kind of the use ,though i have got to know that if it is used i this way it means that it belongs to two kinds of use one it to use as a datatype ,another is to finish the function as it intends to .i want your opinoin,ok? much appreciation !
Regards
jolley