Your question is not Irrlicht specified, but some general UI code design question.
I don't know if there is any tutorial, but I myself often use the concept of "scene".
A scene is a virtual concept that you draw on. A scene is an object, it renders any stuff that should display on the scene, and never cares how other scenes work.
So in your question, you may have a main menu scene, an options menu scene, a credits scene, a game scene (the game scene is so complicated that you may want to split it to loading scene, game play scene, etc).
In your main menu scene, the scene only renders all the buttons you mentioned above, of course beside the background. In credits scene, the scene may animate your credits names.
When "credits" button is clicked on main menu scene, the scene is swtiched to credit scene. That's to say, your whole game is just switching between scenes.
Just some basic beginning ideas.