Installation instructions:

Download the Blender file and all 3 zip files into a single directory somewhere on your computer. Unzip the images so that they are one folder down from the Blender file, with no additional sub-folders.

Open Blender, go to the Preferences and in the File Paths tab add the folder into which you installed the Sun And Sky add-on, and name this Sun And Sky. 

If you now open the Asset Browser in Blender and select the Sun and Sky, you can drag-and-drop the environment into your scenes.

Once added there will be a large Empty in the scene, select this and go to the Object tab in the Properties panel and you will be able to access all the controls. You can rotate the sky, change the time of day, the brightness, and the amount of cloud cover.

It is highly recommended to watch the installation and demo videos to see all this in action.