Translation:If it is sunny, then it is not cloudy.
In Dutch this is called an als-dan construction. When/If A, then B. When/If it is sunny (A), then it is not cloudy (B). But 'Als het zonnig is, is het niet bewolkt' is a correct dutch sentence as well. 'Als het zonnig is, dan het niet bewolkt is' isn't a correct sentence. The 'dan' indeed does not change the word order, which isn't the case in this English sentence either. If it is sunny, (then) it is not cloudy. '..., dan [verb] - rest of the sentence'. There might be exceptions on that rule, but as far as I can think of now it is pretty much always a verb after 'dan'. Sorry if the answer isn't sufficient, but I tried ;) Good luck!