Creating links between tables is now easily done in the Field Settings for the target table. The links can also be managed and subsequent Lookups or Roll-ups created in the Field Settings for the target table.
To manage these fields, highlight any table and click on app settings, then choose fields.
There are three options when creating new fields:
Link to another record - This will find a related record in another table to link.
Lookup related value - display the value of a field from a related record.
Roll-up related records - summarize data from records that are linked to the particular table.