It's virtually impossible--and certainly impractical--for anyone to learn and remember everything there is to know about the computer hardware and software they use to do their job. Nearly every computer user needs help at one time or another.
Online help, unlike a printed manual, has the power of the computer at its disposal. Most importantly, this power makes it possible to adapt the information to the user's current "context." Context-sensitive help provides just enough help to get the user back on task. In developing your online help, remember that users need different types of help at different times. By anticipating users' questions, you can design your application help to respond in a logical and intuitive manner.