The easy answer is to select them in the Folder Pane on the left side of the window. Maybe you are missing the Folder Pane. Press the alt key if your Menu Bar is not showing. From the Menu Bar select View-Layout-Folder Pane

When I go to Menu Bar >View > all the options are greyed over! Ken

Reboot your computer. Hold the Shift key while starting Thunderbird to start in safe mode with addons disabled. Any improvement?