Customization > Centers and Tabs > Center Tabs > New
In the Label field, enter a name for the tab. From the Center list, select the center which need to add the tab.
Under audience subtab, select the areas and who have the access to particular center tab.
Under content subtab, click portlet > Select the portlets you need to add > Select column enter left, right, or center to define the location where the portlet appears on the tab. > Check show box
Then save. We can see the added Center Tab on where we added.