To install the Sketch3D addons you first must obtain and install the SketchUp 3D rendering program. It will need to be the locally installed version of SketchUp and not the web-based version.
Once SketchUp has been installed, you can then move on to downloading and installing the various Sketch3D addons into the SketchUp program.
Full instructional videos for the installation of the various addons can be found in our knowledgebase at the link below.