https://developer.salesforce.com/trailhead/force_com_introduction/data_management/data_import
I've tried 5-6 times now to use import wizard to import the file provided for the Data Management Module of Force.com Basics.  It just continues to give me an "There was a problem uploading the CSV file. Try again, or choose another file."  I've tried this on both a PC and a Mac, Chrome and Firefox and browsing to the file or drag and dropping the file, just get the same error every time.