Instructions
Log in to your "World of Warcraft" account and character you want to add the pet toolbar to.
Type "bartender" and press the "Enter" key. A small window will appear.
Click "Pet Bar" on the left side of the window's pane.
Click the "Visibility" tab from the top of the window.
Click any check boxes that are currently checked to un-hide the toolbar. There may be several checks keeping the toolbar from displaying at certain times, such as when inside of a vehicle.
Press the "Close" button at the bottom right of the screen. This will save your changes and make the pet toolbar appear on your character's interface.