Its a way to acces data from your jsppage in your controller. Say you have a form and you want to save the values of that form to the database, @ModelAtribute would be the way to go.
For example this a way to register I wrote a while back:
First in the get method you put your form in a map:
Then in the post method you can bind the map to a entity and save that entity to the database:
Hope this clarified it a bit...
It's good to be able to use someting, it's better to understand how it works.