Hi Lee Sok Har!
Enter the function using the Insert Function dialog.
In Excel 2002 onwards you can use:
Tools > Options > General
Check "Function Tooltips"
OK
And if you email direct I'll send you a Functions List file that gives
source, classifications, descriptions, syntax and argument
descriptions for all Excel and Analysis ToolPak functions. It includes
direct links into help for each function. There's also an (incomplete)
translation of the function names and descriptions.