Assuming that you can see the other worksheet (it's open on your computer)
1. place the cursor where you want to see the data from the other worksheet, then
2. press the = sign
3. go to the cell with the data in the other worksheet and
4. click on it
5. press enter
Would suggest putting the two separate Excel files in a single folder first and then keep them together so they will find each other when opened again. Which is why in any single workbook you can have up to 256 separate worksheets... another option.