Best source for instruction on using "ifthen" formulas in excel?

[JSW formulas]

I need some good information on using different formulas, specifically
"if,then". I have used them in past and generally understand the logic, but
do not know the exact structuring of these formulas.

 

[Dave Peterson]

How about Excel's help?

Or a book?
Debra Dalgleish has a list:
http://www.contextures.com/xlbooks.html

John Walkenbach's book
http://www.amazon.com/gp/explorer/0764540734/2/ref=pd_lpo_ase/103-0377768-3430242?ie=UTF8
gets nice reviews around here.

But if you have a specific question about a specific formula, you may want to
post the formula here with your question.