Thanks, I appreciate the replies.
I don’t want to watch any more YouTube videos. They are all basically impossible to follow unless you already know what they are talking about.
About the four-sided figure that I was making - when the lengths of four sides are specified, and no more, then one can make an infinite number of these figures, because a fifth piece of info needs to be provided to specify the figure uniquely. I figured I could start with an arbitrary four-sided figure and then deform it until it looked like what I wanted. Imagine if I could lock the dimensions of the edges and lock the ends together, and then skew the figure as needed. That would have got me what I wanted. But I did not get that far.
Using the pencil tool and typing in the numbers does not work because it gets me four lines forming an open figure.
Ultimately what I wanted to do is make a bilaterally symmetrical box with edges having different but known lengths. And I tried that by making a rectangle, pulling it into a box, turning it into a component, copying it and flipping the copy, and mating the copy with the original. That gave me my symmetrical box, but with all the edges the wrong size. So I selected edges and moved them around trying to get the right sizes and angles. Two of those edges seemed to work, but the third balked and would not move where it was supposed to go. Then the other edges started to move on me. Erased everything and tried it over again a few times, without success in the end.
That’s when I thought I’d try the irregular 4-sided figure, with the objective of pulling it into a box, getting the right sized edges, and going from there.
The whole point for me to try this in SketchUp was because I ASSUMED it would be capable and allow me to easily modify 3-D objects and edges as required. I think my assumption was wrong.
I already have almost the whole thing drawn out (in 2-D) in PowerPoint. The problem in PowerPoint is that it is not friendly when you need to change dimensions while fine-tuning a design.
But SketchUp is also unfriendly, from what I have seen so far. Lots of hype, fun to work with if you see it as a game to make houses with porches and stairs. But it is a ■■■■■■■ if you think you can easily make 3D forms with precise shapes.
Another problem with SketchUp is that there is apparently no conventional manual. That means there’s no index, so it is not possible to look up specific things. Instead you have to search the Web for something like Edit Rectangle, and you get 1000 hits for MAKING rectangles and zero for editing them.
Therefore it starts to look like I have to read that Dummies book and view countless videos in the hopes of learning enough to do simple tasks.
In short, learning this program is going to take some serious study and practice and time.
I appreciate the advice and the links, I think you guys are knowledgeable and committed. I will have a look at them (except for the videos). But first, I’m going to forget about SketchUp for a few days and see how I feel about it then.