SketchUp is a 3D drawing tool. I am a big fan of the 2D open source software Inkscape. But sometimes I use the free version of SketchUp Make 2017 to do simple 3D drawings.
Most of my knowledge of SketchUp is from a youtube video and the notes shown below.
Youtube Video - Sketchup BASICS for Woodworkers
You can still download a copy of the SketchUp Make 2017 from this web link.
https://help.sketchup.com/en/downloading-older-versions