Using Writer my typing suddenly changed to brown and did not respond to commands

underline and strike through appear apparently at random if i try del or back and there is a vertical line in the LH margin

You have turned on Track Changes, to turn it off press Ctrl+Shift+C or click Edit > Track Changes > Record to unhighlight it. After that click Edit > Track Changes > Accept all to accept the changes that you made while track changes was turned on.