Linking custom fields to entities

Hi,

I am trying to understand how custom fields are linked to records in main entity tables.

For example, we have a custom field that is used in all our customer records.

The Data Model of Entities would indicate that the "CustomField2 entity reference" is where custom fields used by the Customer entity are stored.

But I am struggling to see how to identify a custom field value that belongs to a specific customer record.

Any pointers on how these link together would be really appreciated.

Thank you