Continuing the discussion from Welcome to our forums! Please introduce yourself :
@Adamwilliams welcome to the SketchUp Community Forum.
In your intro post you mentioned figuring out how to install extensions in SU2021. The difference from the ancient SU8 is that you can get many extensions from the Extension Warehouse. In SketchUp, go to Window>Extension Warehouse and search for them. Then just click Install.
Not all extensions are hosted in the Extension Warehouse. Some like those by Fredo6 are hosted at Sketchucation (and Curviloft is still available.) Go to Sketchucation and download the Sketchucation Extension Store. Install it by going to Window>Extension Manager and clicking on Install Extension at the bottom. Navigate to where you saved the downloaded file, select it, and click Open. Once it is installed you can search the Sketchucation extension repository for the desired extensions and again install them.
Remember that many of Fredo6’s extensions like Curviloft require the installation of LibFredo6, too.