Scenes are where you put together all your assets (models, maps, animations and scripts) to create gameplay.
A scene is a tree of game objects which can be parented to one another. Game objects can be positioned, oriented and scaled in the scene, and can have multiple components to display models, maps or execute scripts.
The Camera component adds a camera to your scene.
In most cases, you'll want to have one (and only one) camera in your scene. Having none will result in the game displaying nothing at all (rarely that you would want).
However, you might want to add a second camera for rendering your game's user interface. Or add several more cameras and set their respective viewports to only a part of the screen to create split-screen multiplayer.
A Model Renderer component displays a model at your game object's location.
A Map Renderer component displays a map at your game object's location.
A Scripted Behavior component runs a script on your game object.
A physics component, which can be manipulated through scripts, it also has some basic settings that must be configured initially.