Please help with the very basics

Please can someone help me with some basics. Ive looked at several tutorial videos on YouTube. I was keen to start. As a complete neophyte to Shapr3D I scrawled several odd scribbles and tried random buttons to see what they do. But after a while decided to settle down and try some serious design.
Well I thought nothing is more basic than a rectangle right? Or so I thought. I chose the option of using 3 points. I drawn a quick small rectangle then input a length of 2000mm and magically it extends to 2000mm, great then I input the other dimension of 1800mm. Immediately the rectangle changes to a triangle??? I tried drawing a rectangle with the diagonal option, but that the same triangular effect. WHY?
The rectangle only has 2 dimensions. Can someone please tell me what the hell is going on here.
I feel I cant even get started with the very, very basics. This is so anti intuitive!

Is it possible, that you have turned off sketch constraints?

Ah! Yes that’s it. Thanks very much for your help. Maybe that should be on by default?
I can see this is going to be a steep learning curve.

Hi and welcome to Shapr3D [S3D] Forum.
The perceived ‘learning curve’ is probably not as steep as estimated on first appraisal.
Be assured there is plenty of willing help here and the official Team are quick to respond as you have already discovered.

You may wish to consider watching the following Videos:

[Shapr3D > Learn > Tutorials](3D Modeling Video Tutorials for All Levels | Shapr3D)

IMHO it is a good idea to watch the first couple, from both Sketching and Simple Bodies, on the largest screen available to you. Simply watch and forget about Sketching until you get a feeling for the pace of presentations.
When happy with the above revert to the iPad.
Run S3D
Tap + Hold on the Browser [Safari?] then drag up and to the right until it opens into a Split Screen view.
Tap on the Browser Address Bar and enter
Hit the Icon [Alternative see ✽ below]:
Menu Menu.png
At top right

[Select/GoTo] Learn > Video Tutorials > Sketching [and later?] Simple Bodies

For a larger view of the Video:
Tap+Hold then drag the Separator Bar to the horizontal mid point on the screen.
Unfortunately this decimates the workspace but it could be worthwhile managing this situation?
Follow along prepared to tap the Pause Button frequently.
Drag the Video back to the position where you got thrown off track.
Repeat as many times as necessary to achieve similar results to those in the presentation(s).
When you have completed a couple of Sketching Videos switch to Simple Bodies if you need a change of scenery.
Work through the remainder in a similar manner.
After following the first couple of Videos you should feel rewarded for your efforts as you acclimatise to S3D. Completion of your first Simple Body you should start to feel relaxed enough to take off on your own.
Do try to complete the two Designs suggested in Simple Bodies, the effort really is worthwhile.

✽ You can view these Videos direct on your iPad:
Hit at top left menu:
Help Help.png

Beginner Course 1 or Beginner Course 2
This is the route to get to grips with most things S3D.
My vision of S3D is that it is like having a Super Multitool at your disposal to machine your material.
Your ‘material’ can be the Rectangle that you have successfully Sketched, with that on your screen Double Tap on the Navigation Cube at top right:
Navigation-Orientation%20Cube Navigation-Orientation Cube.png
Your Rectangle with move into a 3D position and the enclosed area should be coloured Light Blue.
Tap within the Light Blue area and drag the Double Arrow pull the Sketch into a Body.
Now you have a chunk of material that can represent anything you want it to, e.g., Metal; Wood; whatever:
Now get to work with that Multitool called S3D.
Tap with your Fingers on a surface of the material and it will move into position square on to your view. It will also resent a Grid on which you can Sketch.
Want to drill a hole? Just select Circle from the Sketch Features menu at the head of the Central Side Menu [note this Menu is user moveable to Left or Right of the screen].
With light pressure place the Pencil tip at the centre of the intended Circle and maintain surface contact while drawing lightly away for the starting point.
With back to 3D view and you have probably guessed tapping on the Circles Light Blue area enables you to push the Arrow through the material to create a hole.
S3D enable you to use Closed Objects, Rectangles; Circles; and many more shapes: to remove material. You may quickly realise that instead of removing this process can also add material.
Searching the Forum can often help with achieving the results, and can be even more efficient than the excellent support available. If you are a ‘Night Owl’ it can save a few hours wait.
Think in 3D and keep experimenting, best wishes for happy S3Ding.

Thanks so much for everyone’s help and advice. It’s all very good and useful advice thanks very much for the help. I have tried the split screen with YouTube tutorials, I’ve also tried watching YouTube whole screen then then trying things out. But the big problem I find is that I can’t see whereabouts on the screen the person is talking about. In other words he might say something like “select your 2 lines then hit button ‘x’ and then…blah blah” this can often happen so quickly that I’m concentrating on the effect and thinking “wow, that looks good’ instead of realising what button/s has been hit to achieve the effect.
It would be mightily handy if there was a highlighted cursor to show exactly what was going on.
But thanks again so much for the help and advice, and so quickly quickly too.

I had exactly the problems that you have experienced, having hearing difficulties did not make it any easier. But still the end result was worth the effort for me.

In the above I said:

Follow along prepared to tap the Pause Button frequently.

and intended to add:

Drag the Video back to the position where you got thrown off track.

Tedious but it can get results. I have added this to my post above.

Unfortunately the Videos need updating to reflect the changes that frequent Updates introduce, it is unlikely that changes will occur until the release of iPadOS because that will introduce improvements that will affect S3D.

Thanks Gelphyn, I like your idea of slowly going through the video. That makes sense, thanks.