Question about Hibernate session.flush()

I want to inquire about what actually the flush method does in the following case:

for (int i = 0; i < myList.size(); i++) {
    Car c = new Car( car.get(i).getId(),car.get(i).getName() );
    getCurrentSession().save(c);
    if (i % 20 == 0)
        getCurrentSession().flush();
}

Does this means that after the iteration 20, the cache is flushed, and then the 20 held memory objects are actually saved in the database ?

Can someone please explain to me what will happen when the condition is true.