Can someone tell me what “Dec 1 St at each end on every fol 6th row until 25 sts remain” means please?

Welcome to KnittingHelp!
If you call the next row, row 1, then you would decrease at [I]each[/I] end on rows 7,13,19,25,31,37,43 etc until there are 25sts on the needle. That’s 2sts decreased per decrease row.