There are multiple ways of reading an .xls file.
1. Add the XLS Reader to the workspace and open the configuration dialog to choose the .xls file from the file system.
2. Drag and drop the .xls file from the file system explorer to the workspace. The XLS Reader node will be created on the workspace automatically and it will be configured to read the dropped file.
Be sure to set the appropriate settings in the configuration dialog according to the file that is read.