Relationship Mapping comes in handy when you have more then one object-type mapped in Bedrock. The most common example is when you have both a Contact and Company mapping.
What this feature will do is it will identify when relationships exist across the different objects so that when we are creating or updating records that live within these objects, we keep these relationships in sync as well. Using the example above of a Contact and Company Mapping, a common relationship is between the contacts that are tied to a given company within each system. The Relationship Mapping feature in Bedrock will make sure that when a company from System A is syncing over to System B, any of the contacts related to System A will remain related over in System B.
Relationship settings exist within each specific mapping (Contact, Company, Opportunity, etc.). When you Auto-Generate your mappings for the first time, all available relationships are automatically setup so there's nothing you necessarily need to do for ensuring these are intact, however, you may want to change up the System of Record order.
To access the settings for Relationships, click on the tab located within each specific mapping (Contact, Company, Opportunity, etc).
Depending on what type of mapping you are in, you may see relationships for companies, owners or contacts:
You can manage the System of Record for relationship mappings just like you would with your field mappings:
If you only have one type of mapping, such as a Contact, then there's only one type of Relationship that you need to worry about and that is Owner relationships. Read up on how Owner Relationships work here.