The menu system makes it much easier for you to create your own menus and manage the way they are shown and hidden based on the game state.

Creating Menus

To create a new menu, add a Simple Menu Manager component to a gameobject in your scene. This is a class that enables you to open and close a menu by calling the Open Menu and Close Menu functions, which enable/disable specified gameobjects that represent the menu.
After you've built the UI for your menu, drag the parent object of the UI into the UI Objects list in the inspector. This gameobject will toggle to enable and disable the menu.
You can also specify the first selected UI object for when the menu is shown, which is useful when using a gamepad or keyboard rather than the mouse.

Opening/Closing Menus Based On Game State

The easiest way to set up menus is to create a game state for them in the Game State Manager. Then, you can use a Game State Enabler component to call the Open Menu function when a specific game state is entered and the Close Menu function when any other game state is entered.