how to map fields in feeds module with csv that has no headers?
The Feeds module support CSV files without column headers.  On admin/structure/feeds/foo_importer/settings/FeedsCSVParser, you just need to select "No Headers".  Then on admin/structure/feeds/foo_importer/mapping, you use the column numbers for the source.

Be careful when entering the Name of source field. Your first column is named '0', the second '1' and so on.