Worry about risk screwing something up by using your reader is wrong thinking. Worst that could happen is delete a book. You should have backup copies of your books or have free download replacement of books you bought. Exploring limits of your reader's settings and use is how you learn how to use all of it's features. Any problems should be easy to correct by yourself maybe at the most with help here at mobileread.com.
If you are trying to root your reader with it could be a little harder to correct mistakes but can be fixed with expert help.
Only easy way to break your reader so it can't be fixed is physical damage by dropping your reader or twisting reader so screen is damaged.