A picture which may or may not explain nesting IF statements.
When I need to create a new formula which might contain nested formulas I always start with typing the following
I then edit the text for each part. Doing it in the this logical (to me) manner helps be build up the correct number of brackets and sections of the statements.
if the first true/false result requires another 'if' statement I'd use the following
The number of nests allowed depends on the flavour of Excel being used.