Installing the OpenCutList SketchUp extension and defining your Preferences.

Installing from the Extension Warehouse

The easiest way to install the signed extension is by downloading it from the OpenCutList by L'Air du Bois extension page at Trimble's Extension Warehouse. The signed file of the latest version is also available on github ladb_opencutlist.rbz.
OpenCutList works with all versions of SketchUp greater than 2017 (the last free version).
Extensions are not available for the online and iPad versions of SketchUp.
After the installation, OpenCutList is accessible via the menu Extensions -> OpenCutList or as an icon on the toolbar. If it does not show up, right-click on an empty area of the icon bar, you should then be able to select it from the list.
OpenCutList in the Toolbar