The tilde symbol just means that two shapes are similar. This means that that the only difference between the two shapes is that they are scaled versions of each other.
This means that the ratio between corresponding sides of the two shapes are the same. We are given a corresponding pair: AD and WZ. The ratio WZ/AD = 56/12. So, all sides in the WXYZ are WZ/AD bigger than the ones in ABCD.
Then to find YZ we have the corresponding side DC = 3. Just multiply that by the ratio WZ/AD and you will get 14.
