Importing data from outside sources is made easier by the options on the Import tab. By choosing one of the Core Tables Buttons you are taken to a layout where you can use standard FileMaker import tools to import data into that table.

To import data from an outside source you may need to pay attention to providing consistent unique identifiers or key fields to allow correctly matching up names, payments, items etc as they are imported into separate tables requiring the key fields to correctly connect the tables.