Meaning: Clouds often have a similar appearance to cotton balls.
Choice of Words: Cotton balls are soft, fluffy balls made of cotton. Look like means to appear similar to something else.
Meaning: The sentence is comparing the texture of clouds to the texture of cotton balls.
Choice of Words: The sentence is saying that clouds are very fluffy.
Meaning: The sentence is comparing the shape of clouds to the shape of cotton balls.
Choice of Words: The sentence is saying that clouds often have a round or oval shape.