You write, "Then I make a tab from another table and add fields to the tab"
Have you allowed records to be created via the relationship? If there is no related record, then there is no field to enter data into...
Double click on the [=] in your relationships graph and look at the buttons on the bottom of the relationships window.
You are correct! I didn't even know this page existed! Wasn't mentioned in Linda.com videos. I tried it aand it worked.
Many many thanks!!