This is simple when you know the trick.
There are fields on a tab page (to the right side of the screen) that show a preview of some fields that are on the tab when you open it.
For example, sales order form:
If you add a new tabPage to this form, you may want these field previews for your fields in your group.
A tabPage has a group under it, with fields in that group.
Go to a field in your group and look at the properties. There is a property called Fast Tab Summary. Set that property to YES and it will show up on your tab page.