This MSAccess tutorial explains the purpose of a tab control in Access 2003 (with screenshots and step-by-step instructions).
A Tab Control is an Access object that allows you to create tabbed pages on an Access form. See picture below.
This is particularly useful if you have more objects (ie: text boxes, combo boxes, etc) than is possible to display on a regular Access form without having to scroll up or down.
A Tab Control can help you display these objects on your Form by displaying tabbed pages. You can then group objects on the various pages.
In this example, we have three tab pages on our Form:
As you can see, the three captions (General, Address, and Shipping Info) appear at the top of the tab control representing each page of the tab control.
(scroll to see more)