It's difficult to obtain car insurance without a U.S. driver's license. While some insurers will offer you a policy with a valid foreign license (never with just an international driver permit or IDP that is only a translation of your license), most will require that you get a U.S. license within a short period of time.
Buying and registering a car can also be tough without an established U.S. credit history and state driver's license, but it can be done. Look for a dealer that is experienced with buyers who have visas and pay cash for the vehicle if possible, since financing when you have only a year on your visa will be difficult.
If you find a car you want to buy, you should contact your state's Department of Motor Vehicles (DMV) to find out what they require from you to register and title a car in your name. This way you won't buy a car and then learn you don't have the right documentation according to the state.
There are some states that require you to have a state identification (ID) card or driver's license in order to title and register a car. Also, most all states require you to show proof of auto insurance when you register your vehicle, so make sure you can get this before buying a car.
Getting insurance with a foreign license isn't easy because car insurance companies can't verify your foreign driving record, years of experience, etc. and so are wary of taking on you as a risk.
There are car insurance providers that will accept your valid foreign driver's license at the inception of a car insurance policy, if you can then provide proof you have obtained a state license within the required time period, which is usually 30 to 45 days from the start of your policy. If you fail to get a state license, then your policy will be canceled.
If you are unable to get a state driver's license, then contact your state's insurance regulator to see if they can advise you on any car insurance companies that do offer coverage to drivers with foreign licenses. There may be specialty auto carriers in your area that do allow this.