SketchUp® is a 3D drawing program available for free from Trimble. You must have a copy of SketchUp® installed on your computer before you can install and use the DrawMetal™ plugins.
Plugins are a means to add features to SketchUp®. There are many plugins available - both for free and for a fee. Plugins are written in the Ruby computer programming language and are often referred to as "Ruby plugins" or "Ruby scripts" or "Ruby Extensions".