The cloud settings tab exposes very simple options for the clouds and has tabs into each effect similarly to surface settings.
Currently Continuum offers 2 layers of clouds though there may be more to come. The Planar Clouds, also known as 2D clouds, are much faster than the 3D clouds, but they don't have any depth to them. The 3D clouds are much more realistic, but also much slower. The layers can be enabled or disabled separately.
Plannar Clouds (WIP)
Combined 2D and 3D
2D cloud density
This setting controls how dense the 2D clouds are. A lower values makes the clouds appear fainter, while a higher values make them more solid. This has no impact on performance and is simply a way to tune the visuals of Continuum
Volumetric Cloud Settings
This setting impacts the overall quality of the clouds. It makes clouds in the distant render more accurately, as you can see from the clouds in the bottom of the pictures below
This setting improves the quality of the direct light (light from the sun) on the 3D clouds. A low values doesn't simulate all the interactions between the clouds and the sunlight, which gives better performance. A higher value performs a full simulation, giving incredibly realistic clouds
Indirect quality is how accurate the indirect light (light that bounces off the earth and other clouds) is. Low makes a lot of guesses about how this light works, and doesn't take information from the world into account, giving clouds a dull look. Medium starts to bring in some information about the world, giving a ballance between performance and realism. High performs a fully accurate simulation, giving the most realistic result
Density controls how dense the clouds are. More dense clouds will block more light, giving darker underside
The coverage setting determines how many clouds are in the sky. This has a minor impact on performance and is mostly so you can tune Continuum to your liking
Altitude determines how high in the sky the clouds are. This setting has no impact on performance