those special characters may have different usages in different operating sys, like the \ is used for directory in windows so they should be avoided in file names
.xlsx / .xls: standard excel formats. xlt: excel template. xlsb: an excel format written in binary instead of xml, which allows for the saving of extremely large spreadsheets faster than standard formats. csv: comma-separated value (as in the first import example used above; can be read by any spreadsheet program).