9.4.4. Buffering Forms question - binder.commit();

My model from the database is pretty big, but there are only a couple of fields that are writable, so tried to implement 9.4.4.
I just started Vaadin last week, so I’m still confused.
I don’t really get how to get my data back (after the user changed it) and pass it back to my database.
I implemented 9.4.4 , but I need more information about what to do with binder.commit();

Do I need to implement beans?
Thanks.