See also help controls.
Context sensitive help is available by pressing the help key in the window. There are two forms of help: a general overview describing what the window does as well as specific help on the key/mouse/menu controls to do it.
Click on the highlighted text to follow the link.
Index is an alphabetical list of all help pages.
Search accepts case insensitive regular expressions.
You can invoke help for a window using the F1 key when the focus is in that window. You can get help for the keyboard/mouse controls using the Shift-F1 key.