If you mean like if you have Workbook.xlsx and Workbook2.xlsx and you want the value from cell A1 of Workbook1 to show up in cell B5 of Workbook2 follow these steps.
Have both Workbook1 and Workbook2 open.
On Workbook2 in cell B5, push the =
then switch to Workbook1 and click in cell A1. You should get the dotted lines around it.
Push enter
Is that what you wanted to do?