What is the exact use of shared_ptr in c++?

#include<iostream>
#include<memory>
#include <vector>

using namespace std;
class x
{
    public:
    int i;
    x():i(12323123)
    {
        cout<<"constructor called"<<endl;
    }
    ~x()
    {
        cout<<"destructor called"<<endl;
    }
};
    vector< shared_ptr<x> > testvec;

int test()
{
        shared_ptr<x> n(new x);
            testvec.push_back((n));
}

main()

{
    test();
    vector< shared_ptr<x> > tests=((testvec));
    cout<<(*(tests.at(0))).i;
}