Yes, you can, you just have to follow the required syntax:
Example:
in "Sheet2" --> Type in cell A1 --> "5"
Then in "Sheet1" in cell B1 ---> "Sheet2!A1" (without quotas)
Now in any cell in "Sheet1" type "=Indirect(B1)"
The result should be "5"... taken from cell A1 in "Sheet2"
You can even link to other files, you just have to stick to the syntax