The following diagram shows how objects in the CDP relate to one another. Native connectors (Salesforce, Marketo, Eloqua) will automatically establish relationships between objects from the same system. For example, the CDP will automatically map the Account Id in the Salesforce Opportunity Object and use it to establish a relationship with Accounts ingested from Salesforce. Similarly, the CDP will automatically map the Lead Id in the Marketo or Eloqua Marketing Activity object and use it to tie the activity data to leads.
The CDP uses the Contact object for both leads and contacts (people records) - they are not differentiated on an object level. Both a Contact Id or Lead Id can be used interchangeably to relate Sales Events, Tasks, and Marketing Activity to contacts in the CDP.