The Netherlands is a member of the Schengen agreement. Depending on your nationality and the length of your stay you may need a visa to enter the Netherlands. Please see the website of the Dutch Ministry of Foreign Affairs for more information: https://www.government.nl/topics/visa-for-the-netherlands-and-the-caribbean-parts-of-the-kingdom
You can apply for a Schengen visa at the Dutch mission (embassy or consulate) in the country where you reside or are entitled to reside. In some countries, you may apply for a visa to an outside agency. You can find the addresses and websites of the Dutch Embassies and Consulates here: http://www.government.nl/issues/embassies-consulates-and-other-representations
It's your own responsibility to apply for visa, Utrecht Summer School doesn't offer any assistance other than a Letter of Acceptance.