Yes, U can practice in USA, even after getting a degree from India. But as someone already said, it is always better to study in USA, if u can. Its not about taking a special exam after medicine, because even if you study in US, u will have to take this exam.(by the way, this exam is called United States Medical Licensing Exam, USMLE & it has 3 parts - steps-1,2&3). But the USMLE scores become much more important, if u do medicine from a school outside US, while for students who did their medicine in US, they are not that important. U will have to score very high in these exams to get into a good residency, if u do medicine from india.
Also, there will be a better chance of u getting into a better speciality if u do ur medicine from US. Unless ur planning to settle down for some low demand specialities like Internal Medicine or Family Medicine, it is always better to do it from USA. You can ask me if u have any more doubts....good luck!