If you can see one or more of your tabs, and simply want to know how to show more tabs, then you can right-mouse button select an existing tab and choose one of the options available for displaying more tabs.
If you have lost all your tabs, such that none are visible, then you can open the Tools-Customize dialog and you'll see every hidden tab display itself. You can then right-mouse button select one of the hidden tabs and choose the "Show Tab" option. Using this technique with the Tools-Customize dialog also gives you access to add any existing toolbar as its own tab by selecting the "Add Tab" option from the right mouse button menu and then picking from the list of available toolbars.
I hope this helps.