To Interpret nested if statement in Excel

Question

Can anyone help me to interpret the following nested if statement in Excel? Thanks.

"The Imputer", "detasian", and "detnphi" are worksheet names of an Excel workbook. cell C9 and cell C10 are user inputs, and cell c16 is a result from an intermediate calculation step.

"value of cell c17"=IF(C16="A",VLOOKUP('The Imputer'!C9&'The Imputer'!C10,detasian!O23:P40,2,FALSE),IF(C16="P",VLOOKUP('The Imputer'!C9&'The Imputer'!C10,detnhpi!L23:M40,2,FALSE),""))

Answer 1

A lookup is performed of C9 concatenated with C10, both from sheet The Imputer in one or other of two ranges, which depending upon whether C16 contains A or P , for the exact match in the adjacent column.

The range for A is sheet detasian O23:P40 and for P sheet detnhpi L23:M40.