This article and related ones are mostly for advanced users who have already implemented the standard events tracking (including the standard entities) as defined in List of tracked events and Examples of web event tracking. If you want to implement custom events tracking (on standard entities) on your website, or tracking standard events on standard entities with custom attributes, this series of articles is for you !
The client-facing standard CDP entities are the following :
There are other entities as well, but they are not relevant for the CDP Webtag and its applications.
You will notice that those entities tie almost perfectly with the standard data feeds. In fact, the standard data feeds are the main way to populate those entities and their attributes : in a sense, you can consider that whatever attribute/entity was configured for your data feeds ingestion can be made available for the CDP Webtag to create/update. So, whatever the schema for your standard data feeds is, it is a pretty good assumption to consider that the objects you are dealing with in the CDP webtag & related APIs will respect that schema (certain exceptions might exist, always check with your CDP team if you have a doubt). Of course, this is a bit simplified :