The tabs that you see on the project screen are also reports.
Your account comes with some default tabs but your administrator can customize them to suit your organization. Open Top Menu ▸ ▸ Admin ▸ Project Management ▸ Project Views and you can add, edit, delete, and reorder the reports. A sample of the project views management screen is show below. Note now the order of the reports corresponds to the order of the project tabs.