Simple..in your destination cell where you want the answer to show up, simply
type "=" (w/o quote). Then go right over to Worksheet 2 and click the cell
you want to subtract from. Then type "-". Then go over to the Worksheet 1
and click on the cell you want to subtract. After clicking that cell, hit
enter. Bam your done. Then you can study the resulting formula if you want
to learn the syntax.
So in my head I say, starting at where I want the answer displayed,
"equals(=) THIS (click on cell) minus (-) THIS (click on cell). Enter."