New text is inserted to the left of the cursor on the entry line. Try this example. When syntax errors are made, helpful messages appear with diagnostic information. You must press ESC to remove the error message before you can make the required changes. There is also a Mode setting that forces all answers to be approximate.
Some menus appear in dialog boxes.
A good example is the MODE menu. Current selections are shown. Arrow right on the first line labeled Graph to see all six possibilities. The F1, F2 and F3 keys open the three pages of the MODE menu. If you exit the box using ESC or any other method, the changes will disappear.