AJAX -- We use it to make pages work cleanly. It cleans up websites, and makes our applications run smoothly. Many projects we have worked on use AJAX...
id of a div or other element that will have the content pushed into
url of page that will be placed into that element
GET or POST (We just use GET)
Just leave an empty string ''
If you have something that will need to be updated constantly.... (for instance the progress information on the image database dashboard) you may use the setInterval javascript function to update the page at intervals (as little as 20 ms works).