I have a MacBook Air w Catalina 10.5. I just downloaded fundamentals from /learn.sketchup.
It’s odd to me that you have to download instructions for something that’s online.
When I try to open it, I get a “file conversion message” that doesn’t seem to make anything work. So I can’t even get in into the help section. Weird and frustrating.
The course files are downloaded as a zip file, and will expand to become a SketchUp_Fundamentals folder in your Downloads folder.
You then watch the course videos online, and at the same time the file used in each lesson is in that downloaded folder. You can open the file for that lesson and follow along with what is shown in the video.
But the files in those download folders don’t open. They look like they are saved as word but the have a .skp extension. When I try to open I get a dialogue box that says, “File conversion” and asks for “encoding that makes your document readable”.
You either need to have SketchUp installed on your machine or open them using SketchUp for Web. Your profile says you are using the free web version. You can start it in your browser and then open the .skp files you’ve extracted from the ZIP file.
If you are using the Web version you don’t have anything in your computer to open SketchUp models. Open the Web version first and open the files from inside it.
A better option is to read the online manual. (At least the “Getting Started” basics.)
Also be aware that the screen shots in the online help can be a bit out of date.
The web edition is constantly being improved and the help images (especially for the menus) lag behind.