You must first decide what column in Spreadsheet A you want to compare with what column in Spreadsheet B.  This is like the keytag in a one to many relationship in a db.  You can use numbers or letters for identifying columns 

So in this example it is comparing Column B (or 2) in Spreadsheet A with column 1 (or A) in Spreadsheet B.  Where the comparision is equal Column B (or 2) from spreadsheet B will be copied to Column J (or 10) in spreadsheet A

SPREADSHEET A

SPREADSHEET B

 

When you press the 'Run' button VBA code will perform the relationship.  If you want to the changes that have been made select the option to highlight the changes made in RED