Topic on Project:Support desk/Flow

How to prepare link to xls file ? That -> When I click path, file xls will be open in Excel.

That depends on having Excel installed in your computer and your browser being condfigured to open it when a .xls file is opened.

If you upload xls files to your wiki (note there is security risk of macro viruses if you let anyone do that), you can link via [[media:Filename.xls]] (assuming user has excel installed)