microsoft+excel+training+course - V lookup

vlookup looks for a certain bit of data in a range of cells and returns a column in that range

if you have a list of customer numbers and you want excel to look for the customer's surname, you can do something like this in cell B2:

=vlookup(A2,Sheet2!A:C,3,0)

looks for whatever is in cell A2 in the range of column A to column C on sheet 2 and returns the 3rd column in the range (column C)