I cant make a formula in sheet 2 using data in sheet 1.

Thanks I will try but I'm not an Excel expert. I am basily clicking in a cell in sheet 2 (Where I want the answer) then going to sheet 1, clicking the cell I want then going to the next cell I want in the foumulare X-Y I wnt in sheet 2 from data in sheet 1. Oddly on parts of sheet 1 I can do this fine and I get the answer in sheet 2 but lower down in sheet 1when I try to do the same the cursor chages to an arrow and I can select the cell.