for_each & ranged base for on 2D array

I was trying to print a 2D array using for_each and range based for loop.

My program goes like this:-

#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
  int a[3][3]={{1,2,3},{4,5,6},{7,8,9}};
  //for_each (begin(a), end(a), [] (int x) { cout<<x<<" ";}); this code throws error

  for_each (begin(a[0]), end(a[2]), [] (int x) { cout<<x<<" ";});  //this code works well, why ?

  cout<<endl;

  for  (auto &row: a)  // without & for row, error is thrown
  {
     for (auto x:row)  // no & needed for x, why ?
     {
        cout<<x<<" ";
     }
  }
  return 0;
}

Why did my first for_each throw errors and why is & symbol necessary for row? What is its type? Is row a pointer?