Define a Primary and a Child Entity Schema

An example of this would be where you have 2 files one for Opportunities and a second for Activities.  In this case, the Primary Entity is OPPORTUNITY and the second Entity is ACTIVITY and they have a relationship.

1. Press the Options button in the top left of the Navigation Bar and select Schemas
2. Press Create Schema button
3. Give the Schema a name - e.g. Opportunity and Activities
4. Select Other as the Source
5. Press Add Primary Entity button
6. Add the Primary Entity Name - eg OPPORTUNITY and specify a Primary Entity Label
7. Specify the column name that is unique for each row as the Primary Key
8. Specify the Sort Order the same as the Primary Key
9. Press the Add Entity button
10. Add the Secondary Entity Name - eg ACTIVITY and specify a Primary Entity Label
11. Specify the column name that is unique for each row as the Primary Key
12. Specify the Sort Order as the Foreign Key to Opportunity followed by its Primary Key
13. Press the Next button
14. Press the Add Relationship button
15. Select OPPORTUNITY as the Entity
16. Select ACTIVITY as the Related Entity
17. Specify the column on the ACTIVITY Entity that is the Foreign Key to OPPORTUNITY - eg OPPORTUNITYID
18. Press the Create button
19. Drill on the Schema and the overview should look like this

Tip:  You can add multiple child Entities related to the Primary Entitiy