In this video describing how sharing works for Google Docs, the Google team explain how we used to share files prior to Google Apps. This video is now reasonably dated and doesn’t explain all the ways that sharing works across the G Suite system.
These ideas also apply to the sharing of other aspects within the Google ecosystem, such as:
Calendar events
Individual files or groups of files
Folders
Other types of files
The key difference for people to get their heads around is that in the past we sent a copy of the document to other people, whereas now we establish a link between a document and other people.
In addition to this, consider the ability to share something with a group of users adds another layer to the possibilities of this powerful collaborative system.