The laws in your state may vary, but usually you'll need to do the following:
Stop at once and see if anyone is injured. Then, call the police for a report. Next, you'll want to exchange information with the other driver.
Obtain from the other driver their name, names of any passengers, vehcile make, model and license plate number and the other drivers insurance information.
It is also a good idea to find any witnesses and take pictures. Your insurance company will like a independent witness that would have a unbiased description. Pictures will always come in handy when making an insurance claim.