Mathematica 9 is now available
Backward Compatibility Note for ? and ??

You can also get information about built-in functions or packages by typing ?Functionname for basic information or ??Functionname for a more detailed explanation. Generally, however, you will be better off consulting the Help Browser. If you use only partial function names, you can use the * wildcard.

Plot         PlotJoined   PlotRange
Plot3D       PlotLabel    PlotRegion
Plot3Matrix  PlotPoints   PlotStyle