My toolbar does not have a "columns" tab, nor can I find an icon to add it by customizing my toolbar.

In the 'View' menu you can directly activate the view 'by Columns'. There you can also activate the 'Toolbar' which contains the icon for the 'by Columns' view.

If the window is narrow, the four buttons may appear as just one Icon with up/down arrows.

The icon will be the current view. Click on it and you can choose the other views.