How to properly install an extension in Site component? Lack of documentation.

Can someone describe to me how to properly install the extension?
The documentation seems to be outdated. According to the new system since v12 extensions should be added using the Sites -> Site Configuration -> Sets for this Site module. However, if resources are added only this way the extension does not load the default settings, {settings} are empty.

Review the Sites → Site Configuration → Sets for this Site workflow described in the issue and compare it with the current extension-installation documentation. Clarify how resources should be added and whether that should load the extension's default settings; done means the documented procedure and the empty {settings} behavior are explained accurately.

Written by the indexing model from the issue text.