Both are Microsoft Word document files. ".docx" is the new file extension that newer Microsoft Word version uses while the older versions save word files as ".doc" files.
One way is to put it in a folder, then open that folder, then go to tools at the top and click it, then click folder options, then click the "View" tab at the top, then scroll down about halfway, and...
No. A docx file is a Word document and a xlsx file is an Excel document. It is possible to copy data from one to the other, like copying a table from Word into Excel, but the files as a whole cannot...