Expression must be a modifiable lvalue - class function [closed]

I was looking to learn some OOP concepts and i'm stuck with this error

#include <iostream>
using namespace std;

class Employee
{
private:
    string name;
    int salary;

public:
    Employee()
    {
        name = "";
        salary = 0;
    }
    int getSalary()
    {
        return salary;
    }
};

int main()
{
    Employee e1;
    e1.getSalary() = 7000;
    cout << e1.getSalary();
    return 0;
}

From what I understood, if I add & to method getSalary() it will be a setter and getter at the same time. I am confused why I need to add & to getSalary() method to work properly. What's the point of reference in this case?