You have chose the "Realistic Skies" option under the "Scene" tab / Atmosphere. Thats a good choice. Now you should click on the "Light" in the "Instances" tab in the right hand tray. Above there you will see "Light   Distant". Click on the little double arrow to the right of that and from the drop down choose "Sun light". Now under the "Scene" tab, look up and see the "Atmosphere" section that says "Realistic skies". Open that section ,if it is not open, and click the "Edit" button. This will open the "Realistic Skies" dialogue control panel. Click the render button to preview your scene. You can click and drag the fuzzy white sun symbol on the blue sky sphere to move the sun around. Checking "auto refresh" will re-render the preview automatically with each scene change.  There are quite a few options here, I suggest you read the manual to find out all the details. You can add more cloud planes of different types, change the cloud planes appearance and height, etc. Set haze, fog, sun color, and lots of other parameters.

 If you select your "ship" back in the main room and then go to the "shader room" by clicking the "paintbrush" icon at the top right of the screen, you should see your shader setup. Again, lots of option here, suggest you start with the manual. Click the "hand " icon up top to return to the "main" or "assembly" room.

Now you should be beginning to understand the "room " concept of Carrara. Different rooms to set up different parts of the scene and a main "Assembly" room for putting them all together.