Remember: Encompass isn't a game engine and it doesn't have a rendering system. So Renderers aren't actually doing the rendering, it is just a way of structuring how we tell the game engine what to render.
A GeneralRenderer is a Renderer which reads the game state in order to draw elements to the screen. It also requires a layer, which represents the order in which it will draw to the screen.
GeneralRenderers are great for things like a heads-up display, where we always want a group of particular elements to be drawn at a specific layer regardless of the specifics of the game state.
An OrderedRenderer provides a structure for the common pattern of wanting to draw an individual Component at a specific layer. OrderedRenderers must specify a component that implements IDrawableComponent.
For 2D games, you will need to use layers to be specific about the order in which elements are drawn to the screen. For a 3D game you will probably end up delegating most of the rendering to some kind of scene/camera system.