We have two grapes here (in the UK) that have been butchered back to the
stump year after year.They have just been steered outside the conservatory,
whereas before they were coming through a hole in the dwarf wall into the
inside.

This year we am letting one shoot run up on each plant, with the aim of
turning it into something useful and decorative.

The question is this, and I don't understand any of the books I have read,
as they assume that we are starting with a new plant:

Part a: can I stop it, ie cut the top off, and if so how far up?

Part b: should I do the same with the bits that come out of the side along
the way, inbetween each leaf and the curly bit that tries to grab on to
stuff?

And of course next year it will set off again from somewhere along the stem,
presumably near the top, and I suppose this must be treated as an extension
of last year's main stem growth.

I am sure it's very simple once you know what you are doing.