For every investment, there is an option to select a layout which will determine which tabs to be shown when an user is opening that investment in CA PPM Classic UI. Let us consider the case for a Project.
There is a default layout present in PPM for the projects which is known as the "Project Default Layout". This exists in the application in the form of a Portlet Page. There are several tabs like Properties, Team, Tasks, Financial Plans etc that we see when we open a project from Home --> Projects. These tabs are created out of the box and arranged in a specific order in that "Project Default Layout" portlet page. The "Properties" tab is selected as the default but an user with admin access can always change the default tab to Team, Tasks or anything else. The admin is also capable of adding a new tab and then making it as the default one.