If you just want to upload an excel file into your app, and store the file. Then the built in file uploader widget will be the best to use. (https://docs.mendix.com/refguide/file-manager/)
If however you want to upload an excel file, and then extract the data from the excel, you will want to use the 'Excel Importer' module. (https://docs.mendix.com/appstore/modules/excel-importer/)
Hope this helps!