Saipan is the capital of the Commonwealth of the Northern Marianas Islands (CNMI). The CNMI is subject to the entry requirements that are layed out by the U.S. Citizenship & Immigration Services. Below are the specific links that are needed for citizens of a Foreign (to the U.S.) country. These links give detailed and specific information on the requirements for individuals from various countries to enter the CNMI, so please ensure that you read the information thoroughly.
U.S. Citizenship & Immigration Service - Visit the U.S.
The above link will take you to a page with general information for visiting the U.S. (including Saipan), and it includes forms and instructions for Extending Your Stay.
U.S. Department of State - Visitor Visas & Visa Waivers
This link gives excellent, in-depth information about who exactly needs a Visitor Visa, how to obtain one, which countries are eligible for Visitor Visa Waivers, and much more! This is definitely the information you need to best prepare for your entry into Saipan.
(We didn't want to just give you a generic link and let you figure it out yourself!)