How do I create a ruleset component? I would like to create a custom ruleset component like the one described in  How to automatically generate multiple aliases for one node?

That answer is for Drupal 7, and I am using Drupal 8. When I go to Rules/Components, none of the plugin options that I see in screenshots of Drupal 7 appear to be available (e.g. rule set, condition set, action set). Basically, the Components tab looks nothing like the one found in Drupal 7, so it's unclear to me how to create a ruleset. I'm not a module developer, but when I look through the module folder, I see a folder named Plugins/RulesExpression which contains files that seem to correspond to these component plugin types. Is there something I have to do to enable them to be available in the administration pages? 

The documentation for Drupal 8 Rules is basically empty. The only documentation I found is for contributing developers; it doesn't seem there is any updated documentation for administrator users of the module, and I have searched far and wide for any insight on this and found nothing.
While Rules components may successfully be created and used programmatically, as of Rules 8.x-3.0-alpha4 there is only minimal support for doing this in the UI. Adding these UI features is part of the last meta task needed to be completed before a beta version of Rules is released. You can discover the current status of these UI porting issues by reading the Rules issue queue at https://www.drupal.org/project/issues/rules