Open a file but cannot draw in it

I have opened a SketchUp file from my PC but I cannot do anything in it like draw a line. I am new to sketchup but have a lot of CAD experience. Does the file need to be saved before beginning to work in it?

Can you share a screenshot?

Actually the UI a little different than in this article, but basically similar…

Other tutorials:

What information is displayed when clicking on the i?