Then I purchased
Amigurume by Alison Hoffman
and the light bulb came on and the problems disappeared.
'Insert a stitch marker into the loop on your hook. Each time you come back around to the stitch marker, move it up to the loop on your hook to begin the next round'.
If you have been confused, like me, it means that as you work any increases/decreases; if they don't fit between the positioning this marker and the chain/stitch to the right of it, you must unpick that round and try again.
The chain/stitch that holds the marker is the first stitch of each round and the chain/stitch to the right of it is the last stitch/chain of the round.