How to convert an Excel file to CSV?

From Excel to Open Office Calc

1. Open your file in Excel or Open Office Calc
2. File -> Save As
3. In the "File Format" menu, select "CSV UTF-8 (Comma-delimited) (.csv)"

From Google Sheets

1. Open your file in Google Sheets
2. File -> Download As
3. Select "Comma-separated values (.csv, current sheet)"
4. If you have more than one sheet, repeat the same operation.