How retrieve element from 1-dimensional array?

There is an array 8×8:

var tiles: [
    1, 3, 3, 3, 1, 1, 3, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 2, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 2, 1, 1, 1, 1,
    1, 1, 1, 1, 2, 1, 1, 1,
    1, 1, 1, 1, 2, 1, 1, 1,
    1, 1, 1, 0, 0, 1, 1, 1
  ];

How to get element by column, row index, I tried this function from network:

getElement(row, column) {
    var index = row * 8 + column; 
}

But I did not get how does this function work, why we multiply on 8 and plus column?