Can someone explain + addTo + ???

Can someone explain + addTo + ???

Hey there. I am going through the Codecademy lessons trying to learn jQuery, and there is a lesson that I have come across where the correct answer includes + addTo +.. i understand the other components of the correct answer, but this piece of code is something that wasn't previously discussed in other lessons on Codecademy, and I am wondering what it means, and what the purpose of it is?  Here is the complete code:

  1.     $(document).ready(function () {
  2.     $("#button").click(function () {
  3.         var toAdd = $('input[name=checkListItem]').val();
  4.         $('.list').append('<div class="item">' + toAdd + "</div>");
  5.     });
  6. });

Any help would be greatly appreciated!

Thanks,
Joe