C++ :: Main Difference Between Pointer And Reference And How To Use Pointers

i'm still unclear between the difference between using pointer and a reference

I understood the concept of pointers in c in the class i took last year

and that was to change the actual value stored in the memory address Code:

void change_a(int a*){
a=6;
}
int main(){
int a=5;
change_a(&a);
}

but in c++ I've been using references in all my assignments because I don't know how to correctly use pointers in c++ I may have missed a class but I'm on spring break and would like to clear things up

so in c++

in my assignments I would call it like this Code:

void change_a(int &a){
a=6;
}
int main(){
int a=5;
change_a(a);
}

so does this change the value in the address or does it make another copy of a in my c++ code and stores 6 in that copy