Hello larrydement,
To link tables, you create a dropdown field linking the tables together. Dropdown fields act as the relationships between the database tables.
Is it that you are looking to add and remove fields from the invoice report? You can select customer information from the field list on the right-hand side of the report. The trick is that you may have the Company table with the Invoice table on the main field list branch. You actually want the Customer info contained in the invoice, which is Invoice.Customer. To access more customer information, you need to put more customer fields on the invoice table.
You technically can't put two tables into one grid. You need to create the relationship between the two tables and have one table receive info from the other table. Here, the invoice table gets the corresponding customer table. To do this, using our scenario, to go Customize -> Tables/Fields -> Invoice. Choose Add a Linked Field and choose the Customer table. (The Customer table is already linked to the invoice table). Then choose the field you want to use on the invoice table. Enter a Display As: name and click Add Field. Click Finished Editing Fields. Refresh the report designer and the field should be available.
'Customer' in the screenshot below is the field that should contain the Customer's name. I believe you need to just drag it over to the screen.
I hope this helps. Let me know if I answered your question.
Greg