Find the Longest Word in a String help me

JavaScript
15

so this is my answer i wish i could understand what its doing.

function findLongestWordLength(str) { 
   var count = str.split(' ');
  var longestWord = 0;

  for (var i = 0; i < count.length; i++) {
    if (count[i].length > longestWord) {
      longestWord = count[i].length;
    }
  }

  return longestWord;
}
  


findLongestWordLength("The quick brown fox jumped over the lazy dog");