A price quote for office equipment. The exchange rate and tax rate sit in B1 and B2, the line totals in column D, and a discount grid sits under the quote. Every task fills a column or a grid, so the result depends on which parts of each reference you lock.
Ask the same question for every reference before you fill: should this part move when the formula is copied? The row number moves when you fill down, the column letter when you fill right. Put $ in front of whatever must stay. In the formula bar, F4 cycles through the four kinds: A1, $A$1, A$1, $A1.