Helen, we have not had success with automatic rating of difficulty level, especially across multiple languages. The best indicator for each learner will always be the "new words" number, once, of course you have created enough LingQs and studied long enough at LingQ to make this indicator accurate for you.
@rae68 - Have you watched the video we made about LingQ 2.0? http://www.youtube.com/watch?v=hkanvt_HU-0 It will give you an idea of how things are supposed to work. Hints save automatically. You just have to hit enter or click away from the hint field. The dictionary window will expand to fill your screen size vertically. There is no way to expand it more than that.
To find all lessons in a course (we call collections courses now) simply click the "View course" link in the info pane on the lesson page or in the dropdown beside the Open button for one of the lessons in the library.