When you first create a table (and its fields), the default layout is created with all those fields. When you add/remove fields from that table, you must manually go to Layout mode and do that (add/remove).
Thank you for your post!
beverly offered great information. If you are in FileMaker Pro 13 or newer you will have a Field Picker in Layout Mode to drag your field onto the Layout. You might see Placing and removing fields on a layout for more information.
I'm also going to move this thread from the FileMaker Community Feedback Space (which is specifically for input on the Community itself) to the Discussions Space where you should receive more views and potentially more feedback on this topic!