Ah, that explains it. Anyway, I managed to do it. It was, as it always seems afterwards, quite easy. But when you start out in working life as I did, using an Underwood manual typewriter, computers can still downface you sometimes.
Anyway, thanks once again for the help. I had actually done it once before but couldn't recall how - I was clicking on the white arrow on the left instead of the little white box on the right.
When that happens I remind myself of my husband, who can stand in front of an open cupboard where the sugar has been kept for thirty years, asking, 'Where have you moved the sugar to this time?' I'll be more sympathetic next time.