If you have a spreadsheet from Works versions 6 and later, you can open it directly in Excel. If you used an even older version, you can re-save the file as an Excel formatted file from within Works.

A ".WKS" file is a Microsoft Works file, containing plain or rich text from the Microsoft Works writing application. While it is beneficial to have Microsoft Works installed to open a ".WKS" file ...

If you cannot open an Excel file and see Excel cannot open the file because the file format or extension is not valid error, see this post.