<?php
$grid = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
];

echo $grid[0][0];   // 1  (row 0, column 0)
echo $grid[1][2];   // 6  (row 1, column 2)
echo $grid[2][1];   // 8  (row 2, column 1)
?>