The United States, Canada and over 100 other countries are party to the International Convention on Road Traffic. This Convention is intended to establish uniform reciprocal privileges on matters such as drivers' permits. The agreement also requires the US and its states to allow a foreign driver admitted to the US to drive a private motor vehicle for one year on certain conditions. The Marshall Islands are not a member of this agreement.
However since the Republic of the Marshall Islands (RMI) is a US Territory it is given some special recognition. The RIM Embassy notes that to reside in the United States, you need a valid (unexpired) RMI passport and an I-94 form (which will be given to you at your port of entry into the United States.). You do not need an Alien Registration Number. As a Marshallese citizen in the US under the Compact of Free Association, you can also apply for a Social Security Card (SSN). Your card should be one without any legend, meaning that it says on it that you are lawfully admitted for permanent residence and are allowed to work in the US.
The RMI Embassy also notes that driver's licenses from the Marshall Islands are valid for up to one year after moving to the U.S. Because regulations vary from state to state, and because laws can change often, if you are planning on staying in the U.S. longer than 3 months, it is advised that you get a US driver’s license as soon as possible. To get a U.S. license, you need to go to the local Department of Motor Vehicles of state in which you are going to reside and present your Marshallese passport and take a written driving test. Currently, the driving test is not offered in Marshallese in any state to the best of our knowledge.
As noted above the regulations regarding a driver's license from the Marshall Islands varies from state to state it is important to contact any states' department of motor vehicles you plan on driving in just to make certain your driver's license from the Marshall Islands will be accepted for the time period which you plan to operate a vehicle in the US.
For example Louisiana notes that US Territories are given reciprocity with regards to driver's license and are exempted from testing if the person applies for a driver's license in LA. They consider the following places as US Territories: Guam, Puerto Rico, U.S. Virgin Islands, American Samoa, Marshall Islands, Palau, Micronesia, and the Mariana Islands.
And the South Carolina DMV notes that drivers from other countries may obtain a South Carolina driver's license without taking a test other than the vision test if South Carolina has reciprocity with their home country. The following countries have reciprocity with South Carolina for noncommercial vehicles: France, Germany, American Samoa, Guam, Puerto Rico and the Virgin Islands, the Federated States of Micronesia, the Republic of the Marshall Islands and the Republic of Palau for regular driver licenses only.
While the RMI embassy notes that a Marshall Island driver's license is accepted in the United States for up to a year if you plan on driving in the US you should contact the DMV of the state's in which you plan to drive. The DMV can verify they accept this driver's license, how long you can operate a vehicle with your RMI license and tell you if they will require you also to carry an international driving permit (IDP).
If you plan on staying in the United States then you should apply for a State license as soon as possible since that will make it easier for you to register and insure a vehicle. Most all insurance carriers require a US license when you want to place insurance on your vehicle here in the US since they need to rate you based on the US license that they can verify information on and not a foreign license which they cannot.