Introducing myself

I am a retired engineer doing volunteer work using EXCEL. On the side I volunteer tutoring people in EXCEL, WORD and LibreOffice. I have pretty well taught myself the things I need to do with EXCEL but am stumped on how to do "do loops" and particularly nested loops. I am trying to find duplicates in a gigantic list of addresses and need to do a comparison check between two columns of addresses arranged on a spread sheet as two 4 column lists of street number, direction, name and unit. The lists are of unequal length.
I can handle the decision functions but have problems with setting up the loop. I am hoping someone can straighten me out. All help is greatly appreciated.

Paul,
Please forgive my misstep. I will post the question properly in programming.
derwalroszsagt