Much of the documentation for Investor/RT is written from the perspective of the Windows version of the software. There is frequent mention of the Alt key, the Ctrl Key and the Delete Key. These are keys typically visible on Windows PC keyboards. On Macintosh PC's the keys are labeled differently (Think Different, as the Apple slogan goes).
The Alt Key is called the Command key on Macintosh keyboards. The symbol on the key typically resembles a cloverleaf. Long time users of Macintosh PCs will remember the days when this key was called the Apple key.
The Ctrl-Key is called the Option Key on Macintosh keyboards. If you see the phrase "Ctrl-click..." this means Option Click for Mac users.
The Delete key is more mysterious. Modern Mac keyboards do have a Delete Key but its function on the Mac is the same as the Backspace key on Windows. It is used to backspace when typing. When Investor/RT documentation says to press the Delete Key, you have to hold down the Function key (Fn Key) on the Mac keyboard and press Delete. Fn-Delete is a forward delete (as opposed to a backspace) and Fn-Delete is equivalent to the Delete Key on Windows PC's. On Windows PC the Delete Key is often labelled as the Del key. For example, to delete an indicator in a chart, first click on the indicator to select it, then press the Del Key on Windows or Fn-Delete on a Macintosh).