As those who respond are all volunteers, it is customary to ask for help, rather than just state what you want.
You also need to remember that no one can see your data or your setup of workbooks etc.
With so little information to go on, the best I can suggest is to look at the VLOOKUP() and HLOOKUP() functions. Look at the Help files for these functions and see if they will do what you want. If not or if you cannot get one of them to work, please send a response to this post and include as much detail as possible about what you want to do, what data is involved and where it is stored.
The term look up data usually implies finding data in one range of cells based on the value in another cell.
If you just want a link to a specific cell, where you already know which cell contains the data, then just select the source cell and copy it. Go to the destination cell (in the other Workbook in your case), and right-click the cell and select 'PasteSpecial...' and click the 'Paste Link' button.
You will get a formula something like this
In this example the destination worksheet cell will display the contents of cell A1 on 'Sheet1' in the Workbook 'Source.xls'.