Rabies is a virus which is transmitted in the saliva of infected animals. It is typically spread by animal bites, which inject the virus into the skin of the victim and then slowly spread back into the brain through the neurons (fibers that carry brain signals to the rest of the body). Once the virus reaches the brain and symptoms begin, it is uniformly fatal - one or two case reports of people surviving rabies do exist, but these were under extreme circumstances and the victims were left with severe brain damage.
Fortunately, rabies can easily be prevented by a vaccine that can be administered after the bite. With proper vaccination, it is thought that 100% of potential rabies cases can be prevented. Common animals in the United States that carry rabies include dogs, skunks and bats. The decision whether or not to administer the vaccine include the nature of the bite, the behavior of the animal, whether or not the animal has been vaccinated against rabies, and whether or not the animal is available for testing. Although only an in-person consultation with a doctor
can determine whether you are eligible for vaccination, based on the story you have told, I believe you will likely need vaccination as the dog is a stray whose vaccination status and behavior are likely to be unknown. I urge you to seek an in-person consultation with a doctor as soon as possible, as the ability to prevent rabies depends on early administration of vaccine.