The tabs for quick switching between the model and the individual layouts are On by default and they display on the bottom of the drawing window.
The display of these tabs can be switched off directly on them by right-clicking and choosing "Hide Layout and Model tabs" from the context menu. You can redisplay the tabs again using the model and layout icons on the bottom AutoCAD status bar - right-click the icon and confirm "Display Layout and Model Tabs":
You can control the tab display also from the Options dialog. On the Display tab you can find the checkbox "Display Layout and Model tabs".
Another way - suitable e.g. for scripts - is to use a control variable. The tab display is controlled by the environment variable ShowTabs. To switch the tabs On or Off, use the commands:
(setenv "ShowTabs" "1")
(setenv "ShowTabs" "0")
Or, in AutoCAD LT: SETENV ShowTabs 1.
Please note that some AutoCAD modes hide these tabs ans layout swithing is forbidden in them - e.g. in the block editor (BEDIT).