I think my question is best described with an Example.

I have cell A1 on Sheet1 (cell currently is blank/empty) that I would like
to link to cell B1 on Sheet2 (cell contains the word CAT).

I go to A1 on Sheet1 and type an = in the function tool bar then I select B1
on Sheet2 and the word CAT appears in A1 on Sheet1. Perfect that is what I
want, however, if I change the word in B1 on Sheet2 to DOG, the word does not
change in A1 on Sheet1. Why not? I want it to, how do I do this?