Can someone please explain the following formula to me?

=IF(B4"A",(IF(E40,VLOOKUP(E4,PUDATA,(IF(B4="M",( HLOOKUP(C4,PUAGE,2)),
(HLOOKUP(C4,PUAGE,2)+1)))),0))," ")

It is taken from cell F4 on the "Input Data" worksheet located at this
URL:

http://www.armystudyguide.com/conten...rd-in-mass.xls

I know how to write Vlookups and this worksheet works fine. I am just
curious to know how the combination of Vlookup and Hlookup works in
case I need to modify some of the scoring parameters in the future.
Thank you in advance for your help.