Thank you all.
No, I've not seen the videos, though to be honest I find videos hard to learn from.
Yes, I'd learnt you use the yellow Reference Point to move things about, and that this the default centre for bi-axially symmetrical entities like rectangle and circles. My problems came from moving things accurately, not knowing this is a deeper function of the Snaps - I'd twigged the basic, direct snap choices like grid and Vertex but was moving entities by co-ordinate calculations.
I've tried to use those SEKE moves but just became even more bogged down because though the Snaps menu gives the code-letters, I can't work out when in the sequence and where, so ended up with very strange results.
Things came to a head when investigating a particular, real-life problem. (This by chance matches an interesting point John Earl makes here.) I am modifying parts of a miniature steam-locomotive built with some un-recorded differences, from drawings in binary fractions of inches. I had to copy the original by redrawing in TurboCAD, overlay that in different line colours with what had I measured as actually made, then use a further over-lay to design improvements in their replacements. Lots of conversion from vulgar to decimal fractions, halving of dimensions, additions and subtractions of co-ordinates... l guessed rightly that TC is designed to do this arithmetic "behind the scenes" for you, but had no idea how, and the on-line Help manual does not Help.
I ought add that "overlay" there does not mean CAD 'Layers'. Just different colours on a single-layer, 2D drawing. I am far from learning the mysteries of Layers!
Many years.... Oh Lor'! Not much hope for me then.
However, your are right. I have understood engineering drawings and used manual drawing for many years, but my knowledge of CAD was confined to seeing drawings made that way, and seeing what it's capable of doing. Trying to learn TurboCAD principles from its on-line manual is like trying to learn to drive from the owner's handbook supplied with the car: it tells you where the controls are, but assumes you understand their meanings, functions and use.
My copy of TurboCAD came with a tutorial on a separate CD - no printed material at all. I made a good start with the exercise it walks you through, despite it not explaining anything, so is just a rote exercise. Unfortunately it contained a strange error by which a certain move would delete the whole drawing!
I use two approaches.
1) I set up basic exercises concentrating on single aspects - like the deeper level of Snap use - just a few simple shapes on a blank template. I've attempted 3D drawings like this, to a very low level - I find 2D basics difficult enough, without all those different but interacting co-ordinate and work-plane systems.
2) As you suggest, trying to draw a real thing I wish to make. This gives a clear aim plus some variety and logic in assembling geometric figures into a meaningful drawing. It also forces you to think about where each entity is meant to go, not just throw it at the image and work on it where it sticks. I have sometimes used work-rounds that give drawings that are useable, but awkward to create and rather rough-and-ready, because this does not use TurboCAD to its full advantage or as it is intended - so are ultimately frustrating.
I have searched for printed manuals but none seem to exist for TurboCAD, and virtually none for CAD generally. I know there are lots of videos about but I don't find videos easy to use. The on-line Manual is very difficult. You really have to know what you are looking for, and it scrolls at Warp Factor Eight. I have helped myself a lot by producing a proper, printed, alphabetical index from its contents page - via Word then Excel - but the Manual still does expect you to understand the concepts before searching for details.
I did not realise there is a difference between an isometric view - with which I have been long familiar -- and a 3D Model, given both anyway rely on essentially an optical illusion on a single plane, irrespective of how the image is created.
I always had a clear idea of what I want to be able to do: draw 3D representations of physical engineering parts and assemblies. This is why I bought TurboCAD. I knew from drawings at work, albeit by a different make, that a comprehensive CAD programme lets you do that, lets you view the item from different angles; and to produce orthographic workshop drawings from them. (Am I right thinking it's actually easier, and intended, to produce the 2D workshop elevations from the 3D image, than the other way round?)
I am not worried about learning to make Gallery-standard artworks. I like the pictures and admire the skill, but that's not my aim, and anyway I am not capable of learning that. I do though have a particular engineering project that's been a challenge (or worse) for far too many years, and I had hoped being able to use CAD's 3D functions to a fair level would help me crack its most intractable problems.
I do read the Forum, but it's mainly very advanced indeed, not really very helpful to a beginner.
Finally John, thank you for your closing compliment about my abilities: you have more faith in them than I do!
Thank you for those instructions. This is the sort of operating detail I need but which is not in the Manual.
I think it would be worth me printing these off!
I've sometimes found that the instructions down there in the corner keep repeating, suggesting that whatever I am doing, is wrong. Another clue is the little chequered flag staying grey. Unfortunately it doesn't tell me where. Turning off "Auto" in Join Polyline gives more work to do but has somewhat diagnostic effects. Other tools simply keep saying "Select first entity...", but give no clue what's wrong.
My main difficulty with TurboCAD's terminology is in it not always according with what I'd expect in technical drawing or think by intuition. This has sometimes meant that when I've gone wrong or misunderstood something, I go off searching ever further from the original problem area.