how an unordered_map is initialized with the values of array

I have come across a code where i get confused , An unordered_map is initialised like below

std::unordered_map<std::string, int> wordMap;

// Inserting elements through an initializer_list
wordMap.insert({ {"First", 1}, {"Second", 2}, {"Third", 3} } );

But what surprise me is the below code

int arr[] = { 1, 5, 2, 1, 3, 2, 1 };
unordered_map<int, int> hash; 
    for (int i = 0; i < n; i++) 
        hash[arr[i]]++;

Here i am not getting how key and value is inserted in the mao