There are no formulas that will copy from one location to another--formulas can
retrieve a value from a cell in another worksheet, though.
='sheet 2'!a1
will retrieve the value from A1 from Sheet 2.
If A1 on sheet 2 is empty, you'll see a 0.
You may like this better:
=if('sheet 2'!a1="","",'sheet 2'!a1)
