Woodrow Wilson contributed to American policy in two major ways.
First, in terms of domestic politics, he was one of the progressive presidents. He got Congress to pass a number of progressive laws. These laws did things to regulate corporations more closely and to reduce the advantages the rich had. Examples of this included the reduction of tariffs that helped big businesses and the introduction of an income tax.
Second, in foreign policy, Wilson created a more idealistic policy for the US. This can be seen most clearly in his actions with regard to WWI. In this case, Wilson tried to use US influence to create a new world order in which peace would be easier to achieve. He did this rather than trying to use US power to do things that were in the selfish interests of the country.