what is the process I should prefer to go and study M.sc(phy) in US after my B.sc

Harsha, first you should shortlist the Universities  that offer M.Sc Physics and then check their admission seasons. Most Universities in the US have 2 admission seasons. Based on that, you need to start preparing atleast a year before. You need to give one of the Language proficiency tests either IELTS, TOEFL or SAT. And based on the score you get, you should apply for colleges. You should have a strong statement of purpose written and sent along with the rest of your documents. Once you receive a response from them, you should apply for a student visa by submitting the required documents from the College. If you have to take an education loan, this also will be the time. And once you get a visa, you should block your flight tickets for a tentative date.