Excel offers several ways to enter a function:
typing and clicking
using the Formula Palette
using the Calculator
There is no “best” way—use the methods that you like most.
Function names are not case sensitive. Sum or sum is the same as SUM . Excel converts all function names to uppercase characters.
Do not include spaces when writing formulas.
When writing formulas with nested functions, it's important to properly match parentheses. Excel helps you by boldfacing or coloring parentheses as you type them. If parentheses don't match, Excel either displays an error message (Figures 9 and 10) or offers to correct the error for you (Figure 11). Sometimes Excel will simply fix the error without displaying a message.